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Changes In Branch vtabDocComments Excluding Merge-Ins
This is equivalent to a diff from b233d0f72d to fcc756f8d0
2015-10-18
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20:28 | Update and improve documentation comments for the native virtual table methods. check-in: 2c6bdf20ea user: mistachkin tags: trunk | |
20:11 | Minor simplification to the previous check-in. Also, correct a comment. Closed-Leaf check-in: fcc756f8d0 user: mistachkin tags: vtabDocComments | |
20:07 | Preserve selected HTML tags when processing the virtual table methods documentation into the CHM file. check-in: 42512a2bfb user: mistachkin tags: vtabDocComments | |
01:51 | Fix typo. check-in: b64cf102ce user: mistachkin tags: trunk | |
00:20 | Work in progress on a tool to update the embedded doc comments for the ISQLiteNativeModule interface. check-in: 44c116ca23 user: mistachkin tags: vtabDocComments | |
00:18 | Move the ISQLiteNativeModule interface to its own file. check-in: b233d0f72d user: mistachkin tags: trunk | |
2015-10-17
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21:09 | Update the included core library documentation. check-in: b57c9d07fc user: mistachkin tags: trunk | |
Added Doc/Special/Core/vtab.html.
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content="text/html; charset=UTF-8"> <title>The Virtual Table Mechanism Of SQLite</title> <style type="text/css"> body { margin: auto; font-family: Verdana, sans-serif; padding: 8px 1%; } a { color: #044a64 } a:visited { color: #734559 } .logo { position:absolute; margin:3px; } .tagline { float:right; text-align:right; font-style:italic; width:300px; margin:12px; margin-top:58px; } .menubar { clear: both; border-radius: 8px; background: #044a64; padding: 0px; margin: 0px; cell-spacing: 0px; } .toolbar { text-align: center; line-height: 1.6em; margin: 0; padding: 0px 8px; } .toolbar a { color: white; text-decoration: none; padding: 6px 12px; } .toolbar a:visited { color: white; } .toolbar a:hover { color: #044a64; background: white; } .content { margin: 5%; } .content dt { font-weight:bold; } .content dd { margin-bottom: 25px; margin-left:20%; } .content ul { padding:0px; padding-left: 15px; margin:0px; } /* Things for "fancyformat" documents start here. */ .fancy img+p 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href="index.html"> <img class="logo" src="images/sqlite370_banner.gif" alt="SQLite Logo" border="0"></a> <div><!-- IE hack to prevent disappearing logo--></div> <div class="tagline">Small. 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Reliable.<br>Choose any three.</div> <table width=100% class="menubar"><tr> <td width=100%> <div class="toolbar"> <a href="about.html">About</a> <a href="sitemap.html">Sitemap</a> <a href="docs.html">Documentation</a> <a href="download.html">Download</a> <a href="copyright.html">License</a> <a href="news.html">News</a> <a href="support.html">Support</a> </div> <script> gMsg = "Search SQLite Docs..." function entersearch() { var q = document.getElementById("q"); if( q.value == gMsg ) { q.value = "" } q.style.color = "black" q.style.fontStyle = "normal" } function leavesearch() { var q = document.getElementById("q"); if( q.value == "" ) { q.value = gMsg q.style.color = "#044a64" q.style.fontStyle = "italic" } } function hideorshow(btn,obj){ var x = document.getElementById(obj); var b = document.getElementById(btn); if( x.style.display!='none' ){ x.style.display = 'none'; b.innerHTML='show'; }else{ x.style.display = ''; b.innerHTML='hide'; } return false; } </script> <td> <div style="padding:0 1em 0px 0;white-space:nowrap"> <form name=f method="GET" action="https://www.sqlite.org/search"> <input id=q name=q type=text onfocus="entersearch()" onblur="leavesearch()" style="width:24ex;padding:1px 1ex; border:solid white 1px; font-size:0.9em ; font-style:italic;color:#044a64;" value="Search SQLite Docs..."> <input type=submit value="Go" style="border:solid white 1px;background-color:#044a64;color:white;font-size:0.9em;padding:0 1ex"> </form> </div> </table> <div class=startsearch></div> <h1 align="center">The Virtual Table Mechanism Of SQLite</h1> <h2>1.0 Introduction</h2> <p>A virtual table is an object that is registered with an open SQLite <a href="c3ref/sqlite3.html">database connection</a>. From the perspective of an SQL statement, the virtual table object looks like any other table or view. But behind the scenes, queries and updates on a virtual table invoke callback methods of the virtual table object instead of reading and writing to the database file. <p>The virtual table mechanism allows an application to publish interfaces that are accessible from SQL statements as if they were tables. SQL statements can do almost anything to a virtual table that they can do to a real table, with the following exceptions: <p> <ul> <li> One cannot create a trigger on a virtual table. <li> One cannot create additional indices on a virtual table. (Virtual tables can have indices but that must be built into the virtual table implementation. Indices cannot be added separately using <a href="lang_createindex.html">CREATE INDEX</a> statements.) <li> One cannot run <a href="lang_altertable.html">ALTER TABLE ... ADD COLUMN</a> commands against a virtual table. </ul> <p>Individual virtual table implementations might impose additional constraints. For example, some virtual implementations might provide read-only tables. Or some virtual table implementations might allow <a href="lang_insert.html">INSERT</a> or <a href="lang_delete.html">DELETE</a> but not <a href="lang_update.html">UPDATE</a>. Or some virtual table implementations might limit the kinds of UPDATEs that can be made. <p>A virtual table might represent an in-memory data structures. Or it might represent a view of data on disk that is not in the SQLite format. Or the application might compute the content of the virtual table on demand. <p>Here are some existing and postulated uses for virtual tables: <ul> <li> A <a href="fts3.html">full-text search</a> interface <li> Spatial indices using <a href="rtree.html">R-Trees</a> <li> Introspect the disk content of an SQLite database file (the <a href="dbstat.html">dbstat virtual table</a>) <li> Read and/or write the content of a comma-separated value (CSV) file <li> Access the filesystem of the host computer as if it were a database table <li> Enabling SQL manipulation of data in statistics packages like R </ul> <h3>1.1 Usage</h3> <p>A virtual table is created using a <a href="lang_createvtab.html">CREATE VIRTUAL TABLE</a> statement. <p><b><a href="syntax/create-virtual-table-stmt.html">create-virtual-table-stmt:</a></b> <button id='x1475' onclick='hideorshow("x1475","x1476")'>hide</button></p> <blockquote id='x1476'> <img alt="syntax diagram create-virtual-table-stmt" src="images/syntax/create-virtual-table-stmt.gif" /> </blockquote> <p>The CREATE VIRTUAL TABLE statement creates a new table called <span class='yyterm'>table-name</span> derived from the class class <span class='yyterm'>module-name</span>. The <span class='yyterm'>module-name</span> is the name that is registered for the virtual table by the <a href="c3ref/create_module.html">sqlite3_create_module()</a> interface. <blockquote><pre> CREATE VIRTUAL TABLE tablename USING modulename; </pre></blockquote> <p>One can also provide comma-separated arguments to the module following the module name: <blockquote><pre> CREATE VIRTUAL TABLE tablename USING modulename(arg1, arg2, ...); </pre></blockquote> <p>The format of the arguments to the module is very general. Each <span class='yyterm'>module-argument</span> may contain keywords, string literals, identifiers, numbers, and punctuation. Each <span class='yyterm'>module-argument</span> is passed as written (as text) into the <a href="vtab.html#xcreate">constructor method</a> of the virtual table implementation when the virtual table is created and that constructor is responsible for parsing and interpreting the arguments. The argument syntax is sufficiently general that a virtual table implementation can, if it wants to, interpret its arguments as <a href="lang_createtable.html#tablecoldef">column definitions</a> in an ordinary <a href="lang_createtable.html">CREATE TABLE</a> statement. The implementation could also impose some other interpretation on the arguments. <p>Once a virtual table has been created, it can be used like any other table with the exceptions noted above and imposed by specific virtual table implementations. A virtual table is destroyed using the ordinary <a href="lang_droptable.html">DROP TABLE</a> syntax. <h4>1.1.1 Temporary virtual tables</h4> <p>There is no "CREATE TEMP VIRTUAL TABLE" statement. To create a temporary virtual table, add the "temp" schema before the virtual table name. <blockcuqote><pre> CREATE VIRTUAL TABLE <b>temp.</b>tablename USING module(arg1, ...); </pre></blockquote> <a name="epovtab"></a> <h4>1.1.2 Eponymous virtual tables</h4> <p>Some virtual tables exist automatically in the "main" schema of every database connection in which their module is registered, even without a <a href="lang_createvtab.html">CREATE VIRTUAL TABLE</a> statement. Such virtual tables are called "eponymous virtual tables". To use an eponymous virtual table, simple use the module name as if it were a table. Eponymous virtual tables exist in the "main" schema only, so they will not work if prefixed with a different schema name. <p>An example of an eponymous virtual table is the <a href="dbstat.html">dbstat virtual table</a>. To use the dbstat virtual table as an eponymous virtual table, simply query against the "dbstat" module name, as if it were an ordinary table. (Note that SQLite must be compiled with the <a href="compile.html#enable_dbstat_vtab">SQLITE_ENABLE_DBSTAT_VTAB</a> option to include the dbstat virtual table in the build.) <blockquote><pre> SELECT * FROM dbstat; </pre></blockquote> <p>A virtual table is eponymous if its <a href="vtab.html#xcreate">xCreate</a> method is the exact same function as the <a href="vtab.html#xconnect">xConnect</a> method, or if the <a href="vtab.html#xcreate">xCreate</a> method is NULL. The <a href="vtab.html#xcreate">xCreate</a> method is called when a virtual table is first created using the <a href="lang_createvtab.html">CREATE VIRTUAL TABLE</a> statement. The <a href="vtab.html#xconnect">xConnect</a> method whenever a database connection attaches to or reparses a schema. When these two methods are the same, that indicates that the virtual table has no persistent state that needs to be created and destroyed. <a name="epoonlyvtab"></a> <h5>1.1.2.1 Eponymous-only virtual tables</h5> <p>If the <a href="vtab.html#xcreate">xCreate</a> method is NULL, then <a href="lang_createvtab.html">CREATE VIRTUAL TABLE</a> statements are prohibited for that virtual table, and the virtual table is an "eponymous-only virtual table". Eponymous-only virtual tables are useful as <a href="vtab.html#tabfunc2">table-valued functions</a>. <p> Note that SQLite versions prior to 3.9.0 did not check the xCreate method for NULL before invoking it. So if an eponymous-only virtual table is registered with SQLite version 3.8.11.1 or earlier and a <a href="lang_createvtab.html">CREATE VIRTUAL TABLE</a> command is attempted against that virtual table module, a jump to a NULL pointer will occur, resulting in a crash. <h3>1.2 Implementation</h3> <p>Several new C-level objects are used by the virtual table implementation: <blockquote><pre> typedef struct sqlite3_vtab sqlite3_vtab; typedef struct sqlite3_index_info sqlite3_index_info; typedef struct sqlite3_vtab_cursor sqlite3_vtab_cursor; typedef struct sqlite3_module sqlite3_module; </pre></blockquote> <p>The <a href="c3ref/module.html">sqlite3_module</a> structure defines a module object used to implement a virtual table. Think of a module as a class from which one can construct multiple virtual tables having similar properties. For example, one might have a module that provides read-only access to comma-separated-value (CSV) files on disk. That one module can then be used to create several virtual tables where each virtual table refers to a different CSV file. <p>The module structure contains methods that are invoked by SQLite to perform various actions on the virtual table such as creating new instances of a virtual table or destroying old ones, reading and writing data, searching for and deleting, updating, or inserting rows. The module structure is explained in more detail below. <p>Each virtual table instance is represented by an <a href="c3ref/vtab.html">sqlite3_vtab</a> structure. The sqlite3_vtab structure looks like this: <blockquote><pre> struct sqlite3_vtab { const sqlite3_module *pModule; int nRef; char *zErrMsg; }; </pre></blockquote> <p>Virtual table implementations will normally subclass this structure to add additional private and implementation-specific fields. The nRef field is used internally by the SQLite core and should not be altered by the virtual table implementation. The virtual table implementation may pass error message text to the core by putting an error message string in zErrMsg. Space to hold this error message string must be obtained from an SQLite memory allocation function such as <a href="c3ref/mprintf.html">sqlite3_mprintf()</a> or <a href="c3ref/free.html">sqlite3_malloc()</a>. Prior to assigning a new value to zErrMsg, the virtual table implementation must free any preexisting content of zErrMsg using <a href="c3ref/free.html">sqlite3_free()</a>. Failure to do this will result in a memory leak. The SQLite core will free and zero the content of zErrMsg when it delivers the error message text to the client application or when it destroys the virtual table. The virtual table implementation only needs to worry about freeing the zErrMsg content when it overwrites the content with a new, different error message. <p>The <a href="c3ref/vtab_cursor.html">sqlite3_vtab_cursor</a> structure represents a pointer to a specific row of a virtual table. This is what an sqlite3_vtab_cursor looks like: <blockquote><pre> struct sqlite3_vtab_cursor { sqlite3_vtab *pVtab; }; </pre></blockquote> <p>Once again, practical implementations will likely subclass this structure to add additional private fields. <p>The <a href="c3ref/index_info.html">sqlite3_index_info</a> structure is used to pass information into and out of the xBestIndex method of the module that implements a virtual table. <p>Before a <a href="lang_createvtab.html">CREATE VIRTUAL TABLE</a> statement can be run, the module specified in that statement must be registered with the database connection. This is accomplished using either of the <a href="c3ref/create_module.html">sqlite3_create_module()</a> or <a href="c3ref/create_module.html">sqlite3_create_module_v2()</a> interfaces: <blockquote><pre> int sqlite3_create_module( sqlite3 *db, /* SQLite connection to register module with */ const char *zName, /* Name of the module */ const sqlite3_module *, /* Methods for the module */ void * /* Client data for xCreate/xConnect */ ); int sqlite3_create_module_v2( sqlite3 *db, /* SQLite connection to register module with */ const char *zName, /* Name of the module */ const sqlite3_module *, /* Methods for the module */ void *, /* Client data for xCreate/xConnect */ void(*xDestroy)(void*) /* Client data destructor function */ ); </pre></blockquote> <p>The <a href="c3ref/create_module.html">sqlite3_create_module()</a> and <a href="c3ref/create_module.html">sqlite3_create_module_v2()</a> routines associates a module name with an <a href="c3ref/module.html">sqlite3_module</a> structure and a separate client data that is specific to each module. The only difference between the two create_module methods is that the _v2 method includes an extra parameter that specifies a destructor for client data pointer. The module structure is what defines the behavior of a virtual table. The module structure looks like this: <blockquote><pre> struct sqlite3_module { int iVersion; int (*xCreate)(sqlite3*, void *pAux, int argc, char **argv, sqlite3_vtab **ppVTab, char **pzErr); int (*xConnect)(sqlite3*, void *pAux, int argc, char **argv, sqlite3_vtab **ppVTab, char **pzErr); int (*xBestIndex)(sqlite3_vtab *pVTab, sqlite3_index_info*); int (*xDisconnect)(sqlite3_vtab *pVTab); int (*xDestroy)(sqlite3_vtab *pVTab); int (*xOpen)(sqlite3_vtab *pVTab, sqlite3_vtab_cursor **ppCursor); int (*xClose)(sqlite3_vtab_cursor*); int (*xFilter)(sqlite3_vtab_cursor*, int idxNum, const char *idxStr, int argc, sqlite3_value **argv); int (*xNext)(sqlite3_vtab_cursor*); int (*xEof)(sqlite3_vtab_cursor*); int (*xColumn)(sqlite3_vtab_cursor*, sqlite3_context*, int); int (*xRowid)(sqlite3_vtab_cursor*, sqlite_int64 *pRowid); int (*xUpdate)(sqlite3_vtab *, int, sqlite3_value **, sqlite_int64 *); int (*xBegin)(sqlite3_vtab *pVTab); int (*xSync)(sqlite3_vtab *pVTab); int (*xCommit)(sqlite3_vtab *pVTab); int (*xRollback)(sqlite3_vtab *pVTab); int (*xFindFunction)(sqlite3_vtab *pVtab, int nArg, const char *zName, void (**pxFunc)(sqlite3_context*,int,sqlite3_value**), void **ppArg); int (*Rename)(sqlite3_vtab *pVtab, const char *zNew); /* The methods above are in version 1 of the sqlite_module object. Those ** below are for version 2 and greater. */ int (*xSavepoint)(sqlite3_vtab *pVTab, int); int (*xRelease)(sqlite3_vtab *pVTab, int); int (*xRollbackTo)(sqlite3_vtab *pVTab, int); }; </pre></blockquote> <p>The module structure defines all of the methods for each virtual table object. The module structure also contains the iVersion field which defines the particular edition of the module table structure. Currently, iVersion is always 1, but in future releases of SQLite the module structure definition might be extended with additional methods and in that case the iVersion value will be increased. <p>The rest of the module structure consists of methods used to implement various features of the virtual table. Details on what each of these methods do are provided in the sequel. <h3>1.3 Virtual Tables And Shared Cache</h3> <p>Prior to SQLite <a href="releaselog/3_6_17.html">version 3.6.17</a>, the virtual table mechanism assumes that each <a href="c3ref/sqlite3.html">database connection</a> kept its own copy of the database schema. Hence, the virtual table mechanism could not be used in a database that has <a href="sharedcache.html">shared cache mode</a> enabled. The <a href="c3ref/create_module.html">sqlite3_create_module()</a> interface would return an error if <a href="sharedcache.html">shared cache mode</a> is enabled. That restriction was relaxed beginning with SQLite <a href="releaselog/3_6_17.html">version 3.6.17</a>. <h3>1.4 Creating New Virtual Table Implementations</h3> <p>Follow these steps to create your own virtual table: <p> <ol> <li> Write all necessary methods. <li> Create an instance of the <a href="c3ref/module.html">sqlite3_module</a> structure containing pointers to all the methods from step 1. <li> Register your <a href="c3ref/module.html">sqlite3_module</a> structure using one of the <a href="c3ref/create_module.html">sqlite3_create_module()</a> or <a href="c3ref/create_module.html">sqlite3_create_module_v2()</a> interfaces. <li> Run a <a href="lang_createvtab.html">CREATE VIRTUAL TABLE</a> command that specifies the new module in the USING clause. </ol> <p>The only really hard part is step 1. You might want to start with an existing virtual table implementation and modify it to suit your needs. There are several virtual table implementations in the SQLite source tree (for testing purposes). You might use one of those as a guide. Locate these test virtual table implementations by searching for "sqlite3_create_module". <p>You might also want to implement your new virtual table as a <a href="c3ref/load_extension.html">loadable extension</a>. <h2>2.0 Virtual Table Methods</h2> <a name="xcreate"></a> <h3>2.1 The xCreate Method</h3> <blockquote><pre> int (*xCreate)(sqlite3 *db, void *pAux, int argc, char **argv, sqlite3_vtab **ppVTab, char **pzErr); </pre></blockquote> <p>This method is called to create a new instance of a virtual table in response to a <a href="lang_createvtab.html">CREATE VIRTUAL TABLE</a> statement. The db parameter is a pointer to the SQLite <a href="c3ref/sqlite3.html">database connection</a> that is executing the <a href="lang_createvtab.html">CREATE VIRTUAL TABLE</a> statement. The pAux argument is the copy of the client data pointer that was the fourth argument to the <a href="c3ref/create_module.html">sqlite3_create_module()</a> or <a href="c3ref/create_module.html">sqlite3_create_module_v2()</a> call that registered the <a href="c3ref/module.html">virtual table module</a>. The argv parameter is an array of argc pointers to null terminated strings. The first string, argv[0], is the name of the module being invoked. The module name is the name provided as the second argument to <a href="c3ref/create_module.html">sqlite3_create_module()</a> and as the argument to the USING clause of the <a href="lang_createvtab.html">CREATE VIRTUAL TABLE</a> statement that is running. The second, argv[1], is the name of the database in which the new virtual table is being created. The database name is "main" for the primary database, or "temp" for TEMP database, or the name given at the end of the <a href="lang_attach.html">ATTACH</a> statement for attached databases. The third element of the array, argv[2], is the name of the new virtual table, as specified following the TABLE keyword in the <a href="lang_createvtab.html">CREATE VIRTUAL TABLE</a> statement. If present, the fourth and subsequent strings in the argv[] array report the arguments to the module name in the <a href="lang_createvtab.html">CREATE VIRTUAL TABLE</a> statement. <p>The job of this method is to construct the new virtual table object (an <a href="c3ref/vtab.html">sqlite3_vtab</a> object) and return a pointer to it in *ppVTab. <p>As part of the task of creating a new <a href="c3ref/vtab.html">sqlite3_vtab</a> structure, this method <u>must</u> invoke <a href="c3ref/declare_vtab.html">sqlite3_declare_vtab()</a> to tell the SQLite core about the columns and datatypes in the virtual table. The <a href="c3ref/declare_vtab.html">sqlite3_declare_vtab()</a> API has the following prototype: <blockquote><pre> int sqlite3_declare_vtab(sqlite3 *db, const char *zCreateTable) </pre></blockquote> <p>The first argument to <a href="c3ref/declare_vtab.html">sqlite3_declare_vtab()</a> must be the same <a href="c3ref/sqlite3.html">database connection</a> pointer as the first parameter to this method. The second argument to <a href="c3ref/declare_vtab.html">sqlite3_declare_vtab()</a> must a zero-terminated UTF-8 string that contains a well-formed <a href="lang_createtable.html">CREATE TABLE</a> statement that defines the columns in the virtual table and their data types. The name of the table in this CREATE TABLE statement is ignored, as are all constraints. Only the column names and datatypes matter. The CREATE TABLE statement string need not to be held in persistent memory. The string can be deallocated and/or reused as soon as the <a href="c3ref/declare_vtab.html">sqlite3_declare_vtab()</a> routine returns. <p>The xCreate method need not initialize the pModule, nRef, and zErrMsg fields of the <a href="c3ref/vtab.html">sqlite3_vtab</a> object. The SQLite core will take care of that chore. <p>The xCreate should return <a href="rescode.html#ok">SQLITE_OK</a> if it is successful in creating the new virtual table, or <a href="rescode.html#error">SQLITE_ERROR</a> if it is not successful. If not successful, the <a href="c3ref/vtab.html">sqlite3_vtab</a> structure must not be allocated. An error message may optionally be returned in *pzErr if unsuccessful. Space to hold the error message string must be allocated using an SQLite memory allocation function like <a href="c3ref/free.html">sqlite3_malloc()</a> or <a href="c3ref/mprintf.html">sqlite3_mprintf()</a> as the SQLite core will attempt to free the space using <a href="c3ref/free.html">sqlite3_free()</a> after the error has been reported up to the application. <p> If the xCreate method is omitted (left as a NULL pointer) then the virtual table is an <a href="vtab.html#epoonlyvtab">eponymous-only virtual table</a>. New instances of the virtual table cannot be created using <a href="lang_createvtab.html">CREATE VIRTUAL TABLE</a> and the virtual table can only be used via its module name. Note that SQLite versions prior to 3.9.0 do not understand eponymous-only virtual tables and will segfault if an attempt is made to <a href="lang_createvtab.html">CREATE VIRTUAL TABLE</a> on an eponymous-only virtual table because the xCreate method was not checked for null. <p> If the xCreate method is the exact same pointer as the <a href="vtab.html#xconnect">xConnect</a> method, that indicates that the virtual table does not need to initialize backing store. Such a virtual table can be used as an <a href="vtab.html#epovtab">eponymous virtual table</a> or as a named virtual table using <a href="lang_createvtab.html">CREATE VIRTUAL TABLE</a> or both. <a name="hiddencol"></a> <h4>2.1.1 Hidden columns in virtual tables</h4> <p>If a column datatype contains the special keyword "HIDDEN" (in any combination of upper and lower case letters) then that keyword it is omitted from the column datatype name and the column is marked as a hidden column internally. A hidden column differs from a normal column in three respects: <p> <ul> <li> Hidden columns are not listed in the dataset returned by "<a href="pragma.html#pragma_table_info">PRAGMA table_info</a>", <li> Hidden columns are not included in the expansion of a "*" expression in the result set of a <a href="lang_select.html">SELECT</a>, and <li> Hidden columns are not included in the implicit column-list used by an <a href="lang_insert.html">INSERT</a> statement that lacks an explicit column-list. </ul> <p>For example, if the following SQL is passed to <a href="c3ref/declare_vtab.html">sqlite3_declare_vtab()</a>: <blockquote><pre> CREATE TABLE x(a HIDDEN VARCHAR(12), b INTEGER, c INTEGER Hidden); </pre></blockquote> <p>Then the virtual table would be created with two hidden columns, and with datatypes of "VARCHAR(12)" and "INTEGER". <p>An example use of hidden columns can be seen in the <a href="fts3.html">FTS3</a> virtual table implementation, where every FTS virtual table contains an <a href="fts3.html#hiddencol">FTS hidden column</a> that is used to pass information from the virtual table into <a href="fts3.html#snippet">FTS auxiliary functions</a> and to the <a href="fts3.html#section_3">FTS MATCH</a> operator. <a name="tabfunc2"></a> <h4>2.1.2 Table-valued functions</h4> <p>A <a href="vtab.html">virtual table</a> that contains <a href="vtab.html#hiddencol">hidden columns</a> can be used like a table-valued function in the FROM clause of a <a href="lang_select.html">SELECT</a> statement. The arguments to the table-valued function become constraints on the HIDDEN columns of the virtual table. <p>For example, the "generate_series" extension (located in the <a href="http://www.sqlite.org/src/artifact?ci=trunk&filename=ext/misc/series.c">ext/misc/series.c</a> file in the <a href="http://www.sqlite.org/src/tree?ci=trunk">source tree</a>) implements an <a href="vtab.html#epovtab">eponymous virtual table</a> with the following schema: <blockquote><pre> CREATE TABLE generate_series( value, start HIDDEN, stop HIDDEN, step HIDDEN ); </pre></blockquote> <p>The <a href="vtab.html#xbestindex">sqlite3_module.xBestIndex</a> method in the implementation of this table checks for equality constraints against the HIDDEN columns, and uses those as input parameters to determine the range of integer "value" outputs to generate. Reasonable defaults are used for any unconstrained columns. For example, to list all integers between 5 and 50: <blockquote><pre> SELECT value FROM generate_series(5,50); </pre></blockquote> <p>The previous query is equivalent to the following: <blockquote><pre> SELECT value FROM generate_series WHERE start=5 AND stop=50; </pre></blockquote> <p>Arguments on the virtual table name are matched to <a href="vtab.html#hiddencol">hidden columns</a> in order. The number of arguments can be less than the number of hidden columns, in which case the latter hidden columns are unconstrained. However, an error results if there are more arguments than there are hidden columns in the virtual table. <a name="xconnect"></a> <h3>2.2 The xConnect Method</h3> <blockquote><pre> int (*xConnect)(sqlite3*, void *pAux, int argc, char **argv, sqlite3_vtab **ppVTab, char **pzErr); </pre></blockquote> <p>The xConnect method is very similar to <a href="vtab.html#xcreate">xCreate</a>. It has the same parameters and constructs a new <a href="c3ref/vtab.html">sqlite3_vtab</a> structure just like xCreate. And it must also call <a href="c3ref/declare_vtab.html">sqlite3_declare_vtab()</a> like xCreate. <p>The difference is that xConnect is called to establish a new connection to an existing virtual table whereas xCreate is called to create a new virtual table from scratch. <p>The xCreate and xConnect methods are only different when the virtual table has some kind of backing store that must be initialized the first time the virtual table is created. The xCreate method creates and initializes the backing store. The xConnect method just connects to an existing backing store. When xCreate and xConnect are the same, the table is an <a href="vtab.html#epovtab">eponymous virtual table</a>. <p>As an example, consider a virtual table implementation that provides read-only access to existing comma-separated-value (CSV) files on disk. There is no backing store that needs to be created or initialized for such a virtual table (since the CSV files already exist on disk) so the xCreate and xConnect methods will be identical for that module. <p>Another example is a virtual table that implements a full-text index. The xCreate method must create and initialize data structures to hold the dictionary and posting lists for that index. The xConnect method, on the other hand, only has to locate and use an existing dictionary and posting lists that were created by a prior xCreate call. <p>The xConnect method must return <a href="rescode.html#ok">SQLITE_OK</a> if it is successful in creating the new virtual table, or <a href="rescode.html#error">SQLITE_ERROR</a> if it is not successful. If not successful, the <a href="c3ref/vtab.html">sqlite3_vtab</a> structure must not be allocated. An error message may optionally be returned in *pzErr if unsuccessful. Space to hold the error message string must be allocated using an SQLite memory allocation function like <a href="c3ref/free.html">sqlite3_malloc()</a> or <a href="c3ref/mprintf.html">sqlite3_mprintf()</a> as the SQLite core will attempt to free the space using <a href="c3ref/free.html">sqlite3_free()</a> after the error has been reported up to the application. <p>The xConnect method is required for every virtual table implementation, though the <a href="vtab.html#xcreate">xCreate</a> and xConnect pointers of the <a href="c3ref/module.html">sqlite3_module</a> object may point to the same function if the virtual table does not need to initialize backing store. <a name="xbestindex"></a> <h3>2.3 The xBestIndex Method</h3> <p>SQLite uses the xBestIndex method of a virtual table module to determine the best way to access the virtual table. The xBestIndex method has a prototype like this: <blockquote><pre> int (*xBestIndex)(sqlite3_vtab *pVTab, sqlite3_index_info*); </pre></blockquote> <p>The SQLite core communicates with the xBestIndex method by filling in certain fields of the <a href="c3ref/index_info.html">sqlite3_index_info</a> structure and passing a pointer to that structure into xBestIndex as the second parameter. The xBestIndex method fills out other fields of this structure which forms the reply. The <a href="c3ref/index_info.html">sqlite3_index_info</a> structure looks like this: <blockquote><pre> struct sqlite3_index_info { /* Inputs */ const int nConstraint; /* Number of entries in aConstraint */ const struct sqlite3_index_constraint { int iColumn; /* Column on left-hand side of constraint */ unsigned char op; /* Constraint operator */ unsigned char usable; /* True if this constraint is usable */ int iTermOffset; /* Used internally - xBestIndex should ignore */ } *const aConstraint; /* Table of WHERE clause constraints */ const int nOrderBy; /* Number of terms in the ORDER BY clause */ const struct sqlite3_index_orderby { int iColumn; /* Column number */ unsigned char desc; /* True for DESC. False for ASC. */ } *const aOrderBy; /* The ORDER BY clause */ /* Outputs */ struct sqlite3_index_constraint_usage { int argvIndex; /* if >0, constraint is part of argv to xFilter */ unsigned char omit; /* Do not code a test for this constraint */ } *const aConstraintUsage; int idxNum; /* Number used to identify the index */ char *idxStr; /* String, possibly obtained from sqlite3_malloc */ int needToFreeIdxStr; /* Free idxStr using sqlite3_free() if true */ int orderByConsumed; /* True if output is already ordered */ double estimatedCost; /* Estimated cost of using this index */ <b>/* Fields below are only available in SQLite 3.8.2 and later */</b> sqlite3_int64 estimatedRows; /* Estimated number of rows returned */ <b>/* Fields below are only available in SQLite 3.9.0 and later */</b> int idxFlags; /* Mask of SQLITE_INDEX_SCAN_* flags */ }; </pre></blockquote> <p>Please note the warnings on the "estimatedRows" and "idxFlags" field. These fields were added with SQLite versions 3.8.2 and 3.9.0, respectively. Any extension that reads or writes these fields must first check that the version of the SQLite library in use is greater than or equal to 3.8.2 or 3.9.0 - perhaps using a call to <a href="c3ref/libversion.html">sqlite3_version()</a>. The result of attempting to access these fields in an sqlite3_index_info structure created by an older version of SQLite are undefined. <p>In addition, there are some defined constants: <blockquote><pre> #define SQLITE_INDEX_CONSTRAINT_EQ 2 #define SQLITE_INDEX_CONSTRAINT_GT 4 #define SQLITE_INDEX_CONSTRAINT_LE 8 #define SQLITE_INDEX_CONSTRAINT_LT 16 #define SQLITE_INDEX_CONSTRAINT_GE 32 #define SQLITE_INDEX_CONSTRAINT_MATCH 64 #define SQLITE_INDEX_SCAN_UNIQUE 1 /* Scan visits at most 1 row */ </pre></blockquote> <p>The SQLite core calls the xBestIndex method when it is compiling a query that involves a virtual table. In other words, SQLite calls this method when it is running <a href="c3ref/prepare.html">sqlite3_prepare()</a> or the equivalent. By calling this method, the SQLite core is saying to the virtual table that it needs to access some subset of the rows in the virtual table and it wants to know the most efficient way to do that access. The xBestIndex method replies with information that the SQLite core can then use to conduct an efficient search of the virtual table. <p>While compiling a single SQL query, the SQLite core might call xBestIndex multiple times with different settings in <a href="c3ref/index_info.html">sqlite3_index_info</a>. The SQLite core will then select the combination that appears to give the best performance. <p>Before calling this method, the SQLite core initializes an instance of the <a href="c3ref/index_info.html">sqlite3_index_info</a> structure with information about the query that it is currently trying to process. This information derives mainly from the WHERE clause and ORDER BY or GROUP BY clauses of the query, but also from any ON or USING clauses if the query is a join. The information that the SQLite core provides to the xBestIndex method is held in the part of the structure that is marked as "Inputs". The "Outputs" section is initialized to zero. <p>The information in the <a href="c3ref/index_info.html">sqlite3_index_info</a> structure is ephemeral and may be overwritten or deallocated as soon as the xBestIndex method returns. If the xBestIndex method needs to remember any part of the <a href="c3ref/index_info.html">sqlite3_index_info</a> structure, it should make a copy. Care must be take to store the copy in a place where it will be deallocated, such as in the idxStr field with needToFreeIdxStr set to 1. <p>Note that xBestIndex will always be called before <a href="vtab.html#xfilter">xFilter</a>, since the idxNum and idxStr outputs from xBestIndex are required inputs to xFilter. However, there is no guarantee that xFilter will be called following a successful xBestIndex. <p>The xBestIndex method is required for every virtual table implementation. <h4>2.3.1 Inputs</h4> <p>The main thing that the SQLite core is trying to communicate to the virtual table is the constraints that are available to limit the number of rows that need to be searched. The aConstraint[] array contains one entry for each constraint. There will be exactly nConstraint entries in that array. <p>Each constraint will correspond to a term in the WHERE clause or in a USING or ON clause that is of the form <blockquote> column OP EXPR </blockquote> <p>Where "column" is a column in the virtual table, OP is an operator like "=" or "<", and EXPR is an arbitrary expression. So, for example, if the WHERE clause contained a term like this: <blockquote><pre> a = 5 </pre></blockquote> <p>Then one of the constraints would be on the "a" column with operator "=" and an expression of "5". Constraints need not have a literal representation of the WHERE clause. The query optimizer might make transformations to the WHERE clause in order to extract as many constraints as it can. So, for example, if the WHERE clause contained something like this: <blockquote><pre> x BETWEEN 10 AND 100 AND 999>y </pre></blockquote> <p>The query optimizer might translate this into three separate constraints: <blockquote><pre> x >= 10 x <= 100 y < 999 </pre></blockquote> <p>For each constraint, the aConstraint[].iColumn field indicates which column appears on the left-hand side of the constraint. The first column of the virtual table is column 0. The rowid of the virtual table is column -1. The aConstraint[].op field indicates which operator is used. The SQLITE_INDEX_CONSTRAINT_* constants map integer constants into operator values. Columns occur in the order they were defined by the call to <a href="c3ref/declare_vtab.html">sqlite3_declare_vtab()</a> in the <a href="vtab.html#xcreate">xCreate</a> or <a href="vtab.html#xconnect">xConnect</a> method. Hidden columns are counted when determining the column index. <p>The aConstraint[] array contains information about all constraints that apply to the virtual table. But some of the constraints might not be usable because of the way tables are ordered in a join. The xBestIndex method must therefore only consider constraints that have an aConstraint[].usable flag which is true. <p>In addition to WHERE clause constraints, the SQLite core also tells the xBestIndex method about the ORDER BY clause. (In an aggregate query, the SQLite core might put in GROUP BY clause information in place of the ORDER BY clause information, but this fact should not make any difference to the xBestIndex method.) If all terms of the ORDER BY clause are columns in the virtual table, then nOrderBy will be the number of terms in the ORDER BY clause and the aOrderBy[] array will identify the column for each term in the order by clause and whether or not that column is ASC or DESC. <h4>2.3.2 Outputs</h4> <p>Given all of the information above, the job of the xBestIndex method it to figure out the best way to search the virtual table. <p>The xBestIndex method fills the idxNum and idxStr fields with information that communicates an indexing strategy to the <a href="vtab.html#xfilter">xFilter</a> method. The information in idxNum and idxStr is arbitrary as far as the SQLite core is concerned. The SQLite core just copies the information through to the <a href="vtab.html#xfilter">xFilter</a> method. Any desired meaning can be assigned to idxNum and idxStr as long as xBestIndex and xFilter agree on what that meaning is. <p>The idxStr value may be a string obtained from an SQLite memory allocation function such as <a href="c3ref/mprintf.html">sqlite3_mprintf()</a>. If this is the case, then the needToFreeIdxStr flag must be set to true so that the SQLite core will know to call <a href="c3ref/free.html">sqlite3_free()</a> on that string when it has finished with it, and thus avoid a memory leak. <p>If the virtual table will output rows in the order specified by the ORDER BY clause, then the orderByConsumed flag may be set to true. If the output is not automatically in the correct order then orderByConsumed must be left in its default false setting. This will indicate to the SQLite core that it will need to do a separate sorting pass over the data after it comes out of the virtual table. <p>The estimatedCost field should be set to the estimated number of disk access operations required to execute this query against the virtual table. The SQLite core will often call xBestIndex multiple times with different constraints, obtain multiple cost estimates, then choose the query plan that gives the lowest estimate. <p>If the current version of SQLite is 3.8.2 or greater, the estimatedRows field may be set to an estimate of the number of rows returned by the proposed query plan. If this value is not explicitly set, the default estimate of 25 rows is used. <p>If the current version of SQLite is 3.9.0 or greater, the idxFlags field may be set to SQLITE_INDEX_SCAN_UNIQUE to indicate that the virtual table will return only zero or one rows given the input constraints. Additional bits of the idxFlags field might be understood in later versions of SQLite. <p>The aConstraintUsage[] array contains one element for each of the nConstraint constraints in the inputs section of the <a href="c3ref/index_info.html">sqlite3_index_info</a> structure. The aConstraintUsage[] array is used by xBestIndex to tell the core how it is using the constraints. <p>The xBestIndex method may set aConstraintUsage[].argvIndex entries to values greater than zero. Exactly one entry should be set to 1, another to 2, another to 3, and so forth up to as many or as few as the xBestIndex method wants. The EXPR of the corresponding constraints will then be passed in as the argv[] parameters to xFilter. <p>For example, if the aConstraint[3].argvIndex is set to 1, then when xFilter is called, the argv[0] passed to xFilter will have the EXPR value of the aConstraint[3] constraint. <p>By default, the SQLite core double checks all constraints on each row of the virtual table that it receives. If such a check is redundant, the xBestFilter method can suppress that double-check by setting aConstraintUsage[].omit. <a name="xdisconnect"></a> <h3>2.4 The xDisconnect Method</h3> <blockquote><pre> int (*xDisconnect)(sqlite3_vtab *pVTab); </pre></blockquote> <p>This method releases a connection to a virtual table. Only the <a href="c3ref/vtab.html">sqlite3_vtab</a> object is destroyed. The virtual table is not destroyed and any backing store associated with the virtual table persists. This method undoes the work of <a href="vtab.html#xconnect">xConnect</a>. <p>This method is a destructor for a connection to the virtual table. Contrast this method with <a href="vtab.html#sqlite3_module.xDestroy">xDestroy</a>. The xDestroy is a destructor for the entire virtual table. <p>The xDisconnect method is required for every virtual table implementation, though it is acceptable for the xDisconnect and <a href="vtab.html#sqlite3_module.xDestroy">xDestroy</a> methods to be the same function if that makes sense for the particular virtual table. <a name="sqlite3_module.xDestroy"></a> <h3>2.5 The xDestroy Method</h3> <blockquote><pre> int (*xDestroy)(sqlite3_vtab *pVTab); </pre></blockquote> <p>This method releases a connection to a virtual table, just like the <a href="vtab.html#xdisconnect">xDisconnect</a> method, and it also destroys the underlying table implementation. This method undoes the work of <a href="vtab.html#xcreate">xCreate</a>. <p>The <a href="vtab.html#xdisconnect">xDisconnect</a> method is called whenever a database connection that uses a virtual table is closed. The xDestroy method is only called when a <a href="lang_droptable.html">DROP TABLE</a> statement is executed against the virtual table. <p>The xDestroy method is required for every virtual table implementation, though it is acceptable for the <a href="vtab.html#xdisconnect">xDisconnect</a> and xDestroy methods to be the same function if that makes sense for the particular virtual table. <a name="xopen"></a> <h3>2.6 The xOpen Method</h3> <blockquote><pre> int (*xOpen)(sqlite3_vtab *pVTab, sqlite3_vtab_cursor **ppCursor); </pre></blockquote> <p>The xOpen method creates a new cursor used for accessing (read and/or writing) a virtual table. A successful invocation of this method will allocate the memory for the <a href="c3ref/vtab_cursor.html">sqlite3_vtab_cursor</a> (or a subclass), initialize the new object, and make *ppCursor point to the new object. The successful call then returns <a href="rescode.html#ok">SQLITE_OK</a>. <p>For every successful call to this method, the SQLite core will later invoke the <a href="vtab.html#xclose">xClose</a> method to destroy the allocated cursor. <p>The xOpen method need not initialize the pVtab field of the <a href="c3ref/vtab_cursor.html">sqlite3_vtab_cursor</a> structure. The SQLite core will take care of that chore automatically. <p>A virtual table implementation must be able to support an arbitrary number of simultaneously open cursors. <p>When initially opened, the cursor is in an undefined state. The SQLite core will invoke the <a href="vtab.html#xfilter">xFilter</a> method on the cursor prior to any attempt to position or read from the cursor. <p>The xOpen method is required for every virtual table implementation. <a name="xclose"></a> <h3>2.7 The xClose Method</h3> <blockquote><pre> int (*xClose)(sqlite3_vtab_cursor*); </pre></blockquote> <p>The xClose method closes a cursor previously opened by <a href="vtab.html#xopen">xOpen</a>. The SQLite core will always call xClose once for each cursor opened using xOpen. <p>This method must release all resources allocated by the corresponding xOpen call. The routine will not be called again even if it returns an error. The SQLite core will not use the <a href="c3ref/vtab_cursor.html">sqlite3_vtab_cursor</a> again after it has been closed. <p>The xClose method is required for every virtual table implementation. <a name="xeof"></a> <h3>2.8 The xEof Method</h3> <blockquote><pre> int (*xEof)(sqlite3_vtab_cursor*); </pre></blockquote> <p>The xEof method must return false (zero) if the specified cursor currently points to a valid row of data, or true (non-zero) otherwise. This method is called by the SQL engine immediately after each <a href="vtab.html#xfilter">xFilter</a> and <a href="vtab.html#xnext">xNext</a> invocation. <p>The xEof method is required for every virtual table implementation. <a name="xfilter"></a> <h3>2.9 The xFilter Method</h3> <blockquote><pre> int (*xFilter)(sqlite3_vtab_cursor*, int idxNum, const char *idxStr, int argc, sqlite3_value **argv); </pre></blockquote> <p>This method begins a search of a virtual table. The first argument is a cursor opened by <a href="vtab.html#xopen">xOpen</a>. The next two arguments define a particular search index previously chosen by <a href="vtab.html#xbestindex">xBestIndex</a>. The specific meanings of idxNum and idxStr are unimportant as long as xFilter and xBestIndex agree on what that meaning is. <p>The xBestIndex function may have requested the values of certain expressions using the aConstraintUsage[].argvIndex values of the <a href="c3ref/index_info.html">sqlite3_index_info</a> structure. Those values are passed to xFilter using the argc and argv parameters. <p>If the virtual table contains one or more rows that match the search criteria, then the cursor must be left point at the first row. Subsequent calls to <a href="vtab.html#xeof">xEof</a> must return false (zero). If there are no rows match, then the cursor must be left in a state that will cause the <a href="vtab.html#xeof">xEof</a> to return true (non-zero). The SQLite engine will use the <a href="vtab.html#xcolumn">xColumn</a> and <a href="vtab.html#xrowid">xRowid</a> methods to access that row content. The <a href="vtab.html#xnext">xNext</a> method will be used to advance to the next row. <p>This method must return <a href="rescode.html#ok">SQLITE_OK</a> if successful, or an sqlite <a href="rescode.html">error code</a> if an error occurs. <p>The xFilter method is required for every virtual table implementation. <a name="xnext"></a> <h3>2.10 The xNext Method</h3> <blockquote><pre> int (*xNext)(sqlite3_vtab_cursor*); </pre></blockquote> <p>The xNext method advances a <a href="c3ref/vtab_cursor.html">virtual table cursor</a> to the next row of a result set initiated by <a href="vtab.html#xfilter">xFilter</a>. If the cursor is already pointing at the last row when this routine is called, then the cursor no longer points to valid data and a subsequent call to the <a href="vtab.html#xeof">xEof</a> method must return true (non-zero). If the cursor is successfully advanced to another row of content, then subsequent calls to <a href="vtab.html#xeof">xEof</a> must return false (zero). <p>This method must return <a href="rescode.html#ok">SQLITE_OK</a> if successful, or an sqlite <a href="rescode.html">error code</a> if an error occurs. <p>The xNext method is required for every virtual table implementation. <a name="xcolumn"></a> <h3>2.11 The xColumn Method</h3> <blockquote><pre> int (*xColumn)(sqlite3_vtab_cursor*, sqlite3_context*, int N); </pre></blockquote> <p>The SQLite core invokes this method in order to find the value for the N-th column of the current row. N is zero-based so the first column is numbered 0. The xColumn method may return its result back to SQLite using one of the following interface: <p> <ul> <li> <a href="c3ref/result_blob.html">sqlite3_result_blob()</a> <li> <a href="c3ref/result_blob.html">sqlite3_result_double()</a> <li> <a href="c3ref/result_blob.html">sqlite3_result_int()</a> <li> <a href="c3ref/result_blob.html">sqlite3_result_int64()</a> <li> <a href="c3ref/result_blob.html">sqlite3_result_null()</a> <li> <a href="c3ref/result_blob.html">sqlite3_result_text()</a> <li> <a href="c3ref/result_blob.html">sqlite3_result_text16()</a> <li> <a href="c3ref/result_blob.html">sqlite3_result_text16le()</a> <li> <a href="c3ref/result_blob.html">sqlite3_result_text16be()</a> <li> <a href="c3ref/result_blob.html">sqlite3_result_zeroblob()</a> </ul> </p> <p>If the xColumn method implementation calls none of the functions above, then the value of the column defaults to an SQL NULL. <p>To raise an error, the xColumn method should use one of the result_text() methods to set the error message text, then return an appropriate <a href="rescode.html">error code</a>. The xColumn method must return <a href="rescode.html#ok">SQLITE_OK</a> on success. <p>The xColumn method is required for every virtual table implementation. <a name="xrowid"></a> <h3>2.12 The xRowid Method</h3> <blockquote><pre> int (*xRowid)(sqlite3_vtab_cursor *pCur, sqlite_int64 *pRowid); </pre></blockquote> <p>A successful invocation of this method will cause *pRowid to be filled with the <a href="lang_createtable.html#rowid">rowid</a> of row that the <a href="c3ref/vtab_cursor.html">virtual table cursor</a> pCur is currently pointing at. This method returns <a href="rescode.html#ok">SQLITE_OK</a> on success. It returns an appropriate <a href="rescode.html">error code</a> on failure.</p> <p>The xRowid method is required for every virtual table implementation. <a name="xupdate"></a> <h3>2.13 The xUpdate Method</h3> <blockquote><pre> int (*xUpdate)( sqlite3_vtab *pVTab, int argc, sqlite3_value **argv, sqlite_int64 *pRowid ); </pre></blockquote> <p>All changes to a virtual table are made using the xUpdate method. This one method can be used to insert, delete, or update. <p>The argc parameter specifies the number of entries in the argv array. The value of argc will be 1 for a pure delete operation or N+2 for an insert or replace or update where N is the number of columns in the table. In the previous sentence, N includes any hidden columns. <p>Every argv entry will have a non-NULL value in C but may contain the SQL value NULL. In other words, it is always true that <tt>argv[i]!=0</tt> for <b>i</b> between 0 and <tt>argc-1</tt>. However, it might be the case that <tt>sqlite3_value_type(argv[i])==SQLITE_NULL</tt>. <p>The argv[0] parameter is the <a href="lang_createtable.html#rowid">rowid</a> of a row in the virtual table to be deleted. If argv[0] is an SQL NULL, then no deletion occurs. <p>The argv[1] parameter is the rowid of a new row to be inserted into the virtual table. If argv[1] is an SQL NULL, then the implementation must choose a rowid for the newly inserted row. Subsequent argv[] entries contain values of the columns of the virtual table, in the order that the columns were declared. The number of columns will match the table declaration that the <a href="vtab.html#xconnect">xConnect</a> or <a href="vtab.html#xcreate">xCreate</a> method made using the <a href="c3ref/declare_vtab.html">sqlite3_declare_vtab()</a> call. All hidden columns are included. <p>When doing an insert without a rowid (argc>1, argv[1] is an SQL NULL), the implementation must set *pRowid to the rowid of the newly inserted row; this will become the value returned by the <a href="c3ref/last_insert_rowid.html">sqlite3_last_insert_rowid()</a> function. Setting this value in all the other cases is a harmless no-op; the SQLite engine ignores the *pRowid return value if argc==1 or argv[1] is not an SQL NULL. <p>Each call to xUpdate will fall into one of cases shown below. Not that references to <b>argv[i]</b> mean the SQL value held within the argv[i] object, not the argv[i] object itself. <blockquote> <dl> <dt><b>argc = 1</b> <dd><p>The single row with rowid equal to argv[0] is deleted. No insert occurs. <dt><b>argc > 1 <br> argv[0] = NULL</b> <dd><p>A new row is inserted with a rowid argv[1] and column values in argv[2] and following. If argv[1] is an SQL NULL, the a new unique rowid is generated automatically. <dt><b>argc > 1 <br> argv[0] ≠ NULL <br> argv[0] = argv[1]</b> <dd><p>The row with rowid argv[0] is updated with new values in argv[2] and following parameters. <dt><b>argc > 1 <br> argv[0] ≠ NULL <br> argv[0] ≠ argv[1]</b> <dd><p> The row with rowid argv[0] is updated with rowid argv[1] and new values in argv[2] and following parameters. This will occur when an SQL statement updates a rowid, as in the statement: <blockquote> <a href="lang_update.html">UPDATE</a> table SET rowid=rowid+1 WHERE ...; </blockquote> </dl> </blockquote> <p>The xUpdate method must return <a href="rescode.html#ok">SQLITE_OK</a> if and only if it is successful. If a failure occurs, the xUpdate must return an appropriate <a href="rescode.html">error code</a>. On a failure, the pVTab->zErrMsg element may optionally be replaced with error message text stored in memory allocated from SQLite using functions such as <a href="c3ref/mprintf.html">sqlite3_mprintf()</a> or <a href="c3ref/free.html">sqlite3_malloc()</a>. <p>If the xUpdate method violates some constraint of the virtual table (including, but not limited to, attempting to store a value of the wrong datatype, attempting to store a value that is too large or too small, or attempting to change a read-only value) then the xUpdate must fail with an appropriate <a href="rescode.html">error code</a>. <p>There might be one or more <a href="c3ref/vtab_cursor.html">sqlite3_vtab_cursor</a> objects open and in use on the virtual table instance and perhaps even on the row of the virtual table when the xUpdate method is invoked. The implementation of xUpdate must be prepared for attempts to delete or modify rows of the table out from other existing cursors. If the virtual table cannot accommodate such changes, the xUpdate method must return an <a href="rescode.html">error code</a>. <p>The xUpdate method is optional. If the xUpdate pointer in the <a href="c3ref/module.html">sqlite3_module</a> for a virtual table is a NULL pointer, then the virtual table is read-only. <a name="xfindfunction"></a> <h3>2.14 The xFindFunction Method</h3> <blockquote><pre> int (*xFindFunction)( sqlite3_vtab *pVtab, int nArg, const char *zName, void (**pxFunc)(sqlite3_context*,int,sqlite3_value**), void **ppArg ); </pre></blockquote> <p>This method is called during <a href="c3ref/prepare.html">sqlite3_prepare()</a> to give the virtual table implementation an opportunity to overload functions. This method may be set to NULL in which case no overloading occurs. <p>When a function uses a column from a virtual table as its first argument, this method is called to see if the virtual table would like to overload the function. The first three parameters are inputs: the virtual table, the number of arguments to the function, and the name of the function. If no overloading is desired, this method returns 0. To overload the function, this method writes the new function implementation into *pxFunc and writes user data into *ppArg and returns 1. <p>Note that infix functions (<a href="lang_expr.html#like">LIKE</a>, <a href="lang_expr.html#glob">GLOB</a>, <a href="lang_expr.html#regexp">REGEXP</a>, and <a href="lang_expr.html#match">MATCH</a>) reverse the order of their arguments. So "like(A,B)" is equivalent to "B like A". For the form "B like A" the B term is considered the first argument to the function. But for "like(A,B)" the A term is considered the first argument. <p>The function pointer returned by this routine must be valid for the lifetime of the <a href="c3ref/vtab.html">sqlite3_vtab</a> object given in the first parameter. <a name="xBegin"></a> <h3>2.15 The xBegin Method</h3> <blockquote><pre> int (*xBegin)(sqlite3_vtab *pVTab); </pre></blockquote> <p>This method begins a transaction on a virtual table. This is method is optional. The xBegin pointer of <a href="c3ref/module.html">sqlite3_module</a> may be NULL. <p>This method is always followed by one call to either the <a href="vtab.html#xcommit">xCommit</a> or <a href="vtab.html#xrollback">xRollback</a> method. Virtual table transactions do not nest, so the xBegin method will not be invoked more than once on a single virtual table without an intervening call to either <a href="vtab.html#xcommit">xCommit</a> or <a href="vtab.html#xrollback">xRollback</a>. Multiple calls to other methods can and likely will occur in between the xBegin and the corresponding <a href="vtab.html#xcommit">xCommit</a> or <a href="vtab.html#xrollback">xRollback</a>. <a name="xsync"></a> <h3>2.16 The xSync Method</h3> <blockquote><pre> int (*xSync)(sqlite3_vtab *pVTab); </pre></blockquote> <p>This method signals the start of a two-phase commit on a virtual table. This is method is optional. The xSync pointer of <a href="c3ref/module.html">sqlite3_module</a> may be NULL. <p>This method is only invoked after call to the <a href="vtab.html#xBegin">xBegin</a> method and prior to an <a href="vtab.html#xcommit">xCommit</a> or <a href="vtab.html#xrollback">xRollback</a>. In order to implement two-phase commit, the xSync method on all virtual tables is invoked prior to invoking the <a href="vtab.html#xcommit">xCommit</a> method on any virtual table. If any of the xSync methods fail, the entire transaction is rolled back. <a name="xcommit"></a> <h3>2.17 The xCommit Method</h3> <blockquote><pre> int (*xCommit)(sqlite3_vtab *pVTab); </pre></blockquote> <p>This method causes a virtual table transaction to commit. This is method is optional. The xCommit pointer of <a href="c3ref/module.html">sqlite3_module</a> may be NULL. <p>A call to this method always follows a prior call to <a href="vtab.html#xBegin">xBegin</a> and <a href="vtab.html#xsync">xSync</a>. <a name="xrollback"></a> <h3>2.18 The xRollback Method</h3> <blockquote><pre> int (*xRollback)(sqlite3_vtab *pVTab); </pre></blockquote> <p>This method causes a virtual table transaction to rollback. This is method is optional. The xRollback pointer of <a href="c3ref/module.html">sqlite3_module</a> may be NULL. <p>A call to this method always follows a prior call to <a href="vtab.html#xBegin">xBegin</a>. <a name="xrename"></a> <h3>2.19 The xRename Method</h3> <blockquote><pre> int (*xRename)(sqlite3_vtab *pVtab, const char *zNew); </pre></blockquote> <p>This method provides notification that the virtual table implementation that the virtual table will be given a new name. If this method returns <a href="rescode.html#ok">SQLITE_OK</a> then SQLite renames the table. If this method returns an <a href="rescode.html">error code</a> then the renaming is prevented. <p>The xRename method is required for every virtual table implementation. <a name="xsavepoint"></a> <h3>2.20 The xSavepoint, xRelease, and xRollbackTo Methods</h3> <blockquote><pre> int (*xSavepoint)(sqlite3_vtab *pVtab, int); int (*xRelease)(sqlite3_vtab *pVtab, int); int (*xRollbackTo)(sqlite3_vtab *pVtab, int); </pre></blockquote> <p> These methods provide the virtual table implementation an opportunity to implement nested transactions. They are always optional and will only be called in SQLite <a href="releaselog/3_7_7.html">version 3.7.7</a> and later. </p> <p> When xSavepoint(X,N) is invoked, that is a signal to the virtual table X that it should save its current state as savepoint N. A subsequent call to xRollbackTo(X,R) means that the state of the virtual table should return to what it was when xSavepoint(X,R) was last called. The call to xRollbackTo(X,R) will invalidate all savepoints with N>R; none of the invalided savepoints will be rolled back or released without first being reinitialized by a call to xSavepoint(). A call to xRelease(X,M) invalidates all savepoints where N>=M. </p> <p> None of the xSavepoint(), xRelease(), or xRollbackTo() methods will ever be called except in between calls to xBegin() and either xCommit() or xRollback(). </p> |
Changes to Doc/buildChm.tcl.
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41 42 43 44 45 46 47 48 49 50 51 52 53 54 | exec fossil.exe sha1sum [file nativename $fileName] } result] == 0} then { return [string trim [lindex [split $result " "] 0]] } return "" } # # HACK: This procedure checks all the "href" attribute values in the specified # core documentation file. For each value, this procedure checks if the # reference conforms to one of the following general categories: # # 1. A relative reference to a named anchor within the same document. # 2. An absolute reference using HTTP or HTTPS. | > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > | 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 | exec fossil.exe sha1sum [file nativename $fileName] } result] == 0} then { return [string trim [lindex [split $result " "] 0]] } return "" } # # NOTE: This procedure unescapes certain HTML tags that are used within the # documentation for the virtual table methods. # proc unescapeHtmlTags { fileName cdata } { # # NOTE: Read all the textual data from the file. # set data [readFile $fileName] # # NOTE: No replacements made yet. # set count 0 # # NOTE: If requested by the caller, unwrap all content contained with XML # CDATA sections as well. # if {$cdata} then { # # NOTE: Grab everything within the CDATA tags and use verbatim. # incr count [regsub -all -- {<![CDATA[(.*?)]]>} $data {\1} data] } # # TODO: Handle all the HTML tags we know may be present in the virtual # table method documentation. This may need adjustments in the # future. # foreach to [list \ {<b>} {</b>} {<br>} {<dd>} {</dd>} {<dl>} {</dl>} {<dt>} \ {</dt>} {<li>} {</li>} {<ol>} {</ol>} {<tt>} {</tt>} \ {<ul>} {</ul>}] { # # NOTE: Figure out the escaped form of this tag and then replace it # with the unescaped form. # set from [string map [list < <\; > >\;] $to] incr count [regsub -all -- $from $data $to data] } # # NOTE: Issue a warning if the HTML tag patterns were not matched. # if {$count == 0} then { puts stdout "*WARNING* File \"$fileName\" has no supported HTML tags" } # # NOTE: If some replacements were performed on the data from the file, # then overwrite it with the new data. # if {$count > 0} then { writeFile $fileName $data } } # # HACK: This procedure checks all the "href" attribute values in the specified # core documentation file. For each value, this procedure checks if the # reference conforms to one of the following general categories: # # 1. A relative reference to a named anchor within the same document. # 2. An absolute reference using HTTP or HTTPS. |
︙ | ︙ | |||
135 136 137 138 139 140 141 | # NOTE: Perform the replacements, if any, keeping track of how many were # done. # incr count [regsub -all -- $pattern $data $subSpec data] } # | > > > > > > > | | < < | 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 | # NOTE: Perform the replacements, if any, keeping track of how many were # done. # incr count [regsub -all -- $pattern $data $subSpec data] } # # NOTE: Issue a warning if the "href" pattern was not matched. # if {$count == 0} then { puts stdout "*WARNING* File \"$fileName\" does not match: href=\"(.*?)\"" } # # NOTE: If some replacements were performed on the data from the file, # then overwrite it with the new data. # if {$count > 0} then { writeFile $fileName $data } } # # HACK: Copy our local [fixed] copy of the MSDN documenter assembly into the # installed location of NDoc3, if necessary. Actually copying the file # will require elevated administrator privileges; otherwise, it will |
︙ | ︙ | |||
292 293 294 295 296 297 298 299 300 301 302 303 304 305 | if {![file isfile $fileName]} then { puts stdout "Cannot find core syntax file: $fileName" exit 1 } transformCoreDocumentationFile $fileName https://www.sqlite.org/ } ############################################################################### set patterns(.hhc,1) {<!--This document contains Table of Contents information\ for the HtmlHelp compiler\.--><UL>} set patterns(.hhp,1) {Default topic=~System\.Data\.SQLite\.html} | > > > > > > > > > > > > > > | 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 | if {![file isfile $fileName]} then { puts stdout "Cannot find core syntax file: $fileName" exit 1 } transformCoreDocumentationFile $fileName https://www.sqlite.org/ } ############################################################################### foreach fileName [glob -nocomplain [file join $temporaryPath \ System.Data.SQLite~System.Data.SQLite.ISQLiteNativeModule*.html]] { set fileName [file join $path $fileName] if {![file isfile $fileName]} then { puts stdout "Cannot find temporary provider file: $fileName" exit 1 } unescapeHtmlTags $fileName false } ############################################################################### set patterns(.hhc,1) {<!--This document contains Table of Contents information\ for the HtmlHelp compiler\.--><UL>} set patterns(.hhp,1) {Default topic=~System\.Data\.SQLite\.html} |
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Added Doc/vtab.tcl.
> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 | ############################################################################### # # vtab.tcl -- # # Written by Joe Mistachkin. # Released to the public domain, use at your own risk! # ############################################################################### proc readFile { fileName } { set file_id [open $fileName RDONLY] fconfigure $file_id -encoding binary -translation binary set result [read $file_id] close $file_id return $result } proc writeFile { fileName data } { set file_id [open $fileName {WRONLY CREAT TRUNC}] fconfigure $file_id -encoding binary -translation binary puts -nonewline $file_id $data close $file_id return "" } proc escapeSubSpec { data } { regsub -all -- {&} $data {\\\&} data regsub -all -- {\\(\d+)} $data {\\\\\1} data return $data } proc englishToList { value } { set result [list] foreach element [split $value "\t\n ,"] { if {[string tolower $element] ni [list "" and or]} then { lappend result $element } } return $result } proc processLine { line prefix } { if {[string length [string trim $line]] == 0 || \ [regexp -- {<h\d(?: |>)} [string range $line 0 3]]} then { return "" } set result $line foreach remove [list \ {<a name=".*?">} {<a href=".*?">} {</a>} {<p>} {</p>}] { regsub -all -- $remove $result "" result if {[string length [string trim $result]] == 0} then { return "" } } foreach escape [list \ {<b>} {</b>} {<br>} {<dd>} {</dd>} {<dl>} {</dl>} {<dt>} \ {</dt>} {<li>} {</li>} {<ol>} {</ol>} {<tt>} {</tt>} \ {<ul>} {</ul>}] { regsub -all -- ($escape) $result {<![CDATA[\1]]>} result } regsub -all -- {≠} $result {\≠} result regsub -all -- {[(?:;)?} $result {[} result regsub -all -- {](?:;)?} $result {]} result regsub -all -- {<( |\"|\d|=)} $result {\<\1} result regsub -all -- {( |\"|\d|=)>} $result {\1\>} result regsub -all -- {<blockquote><pre>} $result <para><code> result regsub -all -- {</pre></blockquote>} $result </code></para> result regsub -all -- {<blockquote>} $result <para><code> result regsub -all -- {</blockquote>} $result </code></para> result return $result } proc extractMethod { name lines pattern prefix indexVarName methodsVarName } { upvar 1 $indexVarName index upvar 1 $methodsVarName methods array set levels {p 0} set length [llength $lines] while {$index < $length} { set line [lindex $lines $index] if {[regexp -- $pattern $line]} then { break; # stop on this line for outer loop. } else { set trimLine [string trim $line]; set data "" if {$levels(p) > 0 && [string length $trimLine] == 0} then { # blank line, close paragraph. if {[info exists methods($name)]} then { # non-first line, leading line separator. append data \n $prefix </para> } else { # first line, no leading line separator. append data $prefix </para> } incr levels(p) -1 } elseif {[string range $trimLine 0 2] eq "<p>"} then { # open tag ... maybe one line? if {[string range $trimLine end-3 end] eq "</p>"} then { set newLine [processLine $line $prefix] if {[string length $newLine] > 0} then { # one line tag, wrap. if {[info exists methods($name)]} then { # non-first line, leading line separator. append data \n $prefix <para> } else { # first line, no leading line separator. append data $prefix <para> } append data \n $prefix $newLine append data \n $prefix </para> } } else { if {[info exists methods($name)]} then { # non-first line, leading line separator. append data \n $prefix <para> } else { # first line, no leading line separator. append data $prefix <para> } set newLine [processLine $line $prefix] if {[string length $newLine] > 0} then { append data \n $prefix $newLine } incr levels(p) } } else { set newLine [processLine $line $prefix] if {[string length $newLine] > 0} then { if {[info exists methods($name)]} then { # non-first line, leading line separator. append data \n $prefix $newLine } else { # first line, no leading line separator. append data $prefix $newLine } } } if {[string length $data] > 0} then { append methods($name) $data } incr index; # consume this line for outer loop. } } } # # NOTE: This is the entry point for this script. # set path [file normalize [file dirname [info script]]] set coreDocPath [file join $path Special Core] set interfacePath [file join [file dirname $path] System.Data.SQLite] set inputFileName [file join $coreDocPath vtab.html] if {![file exists $inputFileName]} then { puts "input file \"$inputFileName\" does not exist" exit 1 } set outputFileName [file join $interfacePath ISQLiteNativeModule.cs] if {![file exists $outputFileName]} then { puts "output file \"$outputFileName\" does not exist" exit 1 } set lines [split [string map [list \r\n \n] [readFile $inputFileName]] \n] set patterns(method) {^<h3>2\.\d+ The (.*) Method(?:s)?</h3>$} set prefix " /// " unset -nocomplain methods; set start false for {set index 0} {$index < [llength $lines]} {} { set line [lindex $lines $index] if {$start} then { if {[regexp -- $patterns(method) $line dummy capture]} then { foreach method [englishToList $capture] { set methodIndex [expr {$index + 1}] extractMethod \ $method $lines $patterns(method) $prefix methodIndex methods } set index $methodIndex } else { incr index } } elseif {[regexp -- {^<h2>2\.0 Virtual Table Methods</h2>$} $line]} then { set start true; incr index } else { incr index } } set data [string map [list \r\n \n] [readFile $outputFileName]] set count 0; set start 0 # # NOTE: These method names must be processed in the EXACT order that they # appear in the output file. # foreach name [list \ xCreate xConnect xBestIndex xDisconnect xDestroy xOpen xClose \ xFilter xNext xEof xColumn xRowid xUpdate xBegin xSync xCommit \ xRollback xFindFunction xRename xSavepoint xRelease xRollbackTo] { # # HACK: This assumes that a line of 71 forward slashes will be present # before each method, except for the first one. # if {$count > 0} then { set start [string first [string repeat / 71] $data $start] } set pattern "" append pattern ^ {\s{8}} "/// <summary>" append pattern {((?:.|\n)*?)} append pattern {\n\s{8}} "/// </summary>" append pattern {(?:(?:.|\n)*?)} append pattern {\n\s{8}[\w]+?\s+?} $name {\($} if {[regexp -nocase -start \ $start -line -indices -- $pattern $data dummy indexes]} then { set summaryStart [lindex $indexes 0] set summaryEnd [lindex $indexes 1] set data [string range $data 0 $summaryStart]$methods($name)[string \ range $data [expr {$summaryEnd + 1}] end] incr count; set start [expr {$summaryEnd + 1}] } else { error "cannot find virtual table method \"$name\" in \"$outputFileName\"" } } if {$count > 0} then { writeFile $outputFileName [string map [list \n \r\n] $data] } exit 0 |
Changes to System.Data.SQLite/ISQLiteNativeModule.cs.
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11 12 13 14 15 16 17 18 | /// <summary> /// This interface represents a virtual table implementation written in /// native code. /// </summary> public interface ISQLiteNativeModule { /// <summary> /// <para> | > > > > > > | | | | | > | | | | | | | | < | | < | | | | | | | | | < | | < | | | | | | | | | > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > | 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 | /// <summary> /// This interface represents a virtual table implementation written in /// native code. /// </summary> public interface ISQLiteNativeModule { /// <summary> /// <para><code> /// int (*xCreate)(sqlite3 *db, void *pAux, /// int argc, char **argv, /// sqlite3_vtab **ppVTab, /// char **pzErr); /// </code></para> /// <para> /// This method is called to create a new instance of a virtual table /// in response to a CREATE VIRTUAL TABLE statement. /// The db parameter is a pointer to the SQLite database connection that /// is executing the CREATE VIRTUAL TABLE statement. /// The pAux argument is the copy of the client data pointer that was the /// fourth argument to the sqlite3_create_module() or /// sqlite3_create_module_v2() call that registered the /// virtual table module. /// The argv parameter is an array of argc pointers to null terminated strings. /// The first string, argv[0], is the name of the module being invoked. The /// module name is the name provided as the second argument to /// sqlite3_create_module() and as the argument to the USING clause of the /// CREATE VIRTUAL TABLE statement that is running. /// The second, argv[1], is the name of the database in which the new virtual table is being created. The database name is "main" for the primary database, or /// "temp" for TEMP database, or the name given at the end of the ATTACH /// statement for attached databases. The third element of the array, argv[2], /// is the name of the new virtual table, as specified following the TABLE /// keyword in the CREATE VIRTUAL TABLE statement. /// If present, the fourth and subsequent strings in the argv[] array report /// the arguments to the module name in the CREATE VIRTUAL TABLE statement. /// </para> /// <para> /// The job of this method is to construct the new virtual table object /// (an sqlite3_vtab object) and return a pointer to it in *ppVTab. /// </para> /// <para> /// As part of the task of creating a new sqlite3_vtab structure, this /// method <u>must</u> invoke sqlite3_declare_vtab() to tell the SQLite /// core about the columns and datatypes in the virtual table. /// The sqlite3_declare_vtab() API has the following prototype: /// </para> /// <para><code> /// int sqlite3_declare_vtab(sqlite3 *db, const char *zCreateTable) /// </code></para> /// <para> /// The first argument to sqlite3_declare_vtab() must be the same /// database connection pointer as the first parameter to this method. /// The second argument to sqlite3_declare_vtab() must a zero-terminated /// UTF-8 string that contains a well-formed CREATE TABLE statement that /// defines the columns in the virtual table and their data types. /// The name of the table in this CREATE TABLE statement is ignored, /// as are all constraints. Only the column names and datatypes matter. /// The CREATE TABLE statement string need not to be /// held in persistent memory. The string can be /// deallocated and/or reused as soon as the sqlite3_declare_vtab() /// routine returns. /// </para> /// <para> /// The xCreate method need not initialize the pModule, nRef, and zErrMsg /// fields of the sqlite3_vtab object. The SQLite core will take care of /// that chore. /// </para> /// <para> /// The xCreate should return SQLITE_OK if it is successful in /// creating the new virtual table, or SQLITE_ERROR if it is not successful. /// If not successful, the sqlite3_vtab structure must not be allocated. /// An error message may optionally be returned in *pzErr if unsuccessful. /// Space to hold the error message string must be allocated using /// an SQLite memory allocation function like /// sqlite3_malloc() or sqlite3_mprintf() as the SQLite core will /// attempt to free the space using sqlite3_free() after the error has /// been reported up to the application. /// </para> /// <para> /// If the xCreate method is omitted (left as a NULL pointer) then the /// virtual table is an eponymous-only virtual table. New instances of /// the virtual table cannot be created using CREATE VIRTUAL TABLE and the /// virtual table can only be used via its module name. /// Note that SQLite versions prior to 3.9.0 do not understand /// eponymous-only virtual tables and will segfault if an attempt is made /// to CREATE VIRTUAL TABLE on an eponymous-only virtual table because /// the xCreate method was not checked for null. /// </para> /// <para> /// If the xCreate method is the exact same pointer as the xConnect method, /// that indicates that the virtual table does not need to initialize backing /// store. Such a virtual table can be used as an eponymous virtual table /// or as a named virtual table using CREATE VIRTUAL TABLE or both. /// </para> /// <para> /// If a column datatype contains the special keyword "HIDDEN" /// (in any combination of upper and lower case letters) then that keyword /// it is omitted from the column datatype name and the column is marked /// as a hidden column internally. /// A hidden column differs from a normal column in three respects: /// </para> /// <para> /// <![CDATA[<ul>]]> /// <![CDATA[<li>]]> Hidden columns are not listed in the dataset returned by /// "PRAGMA table_info", /// <![CDATA[<li>]]> Hidden columns are not included in the expansion of a "*" /// expression in the result set of a SELECT, and /// <![CDATA[<li>]]> Hidden columns are not included in the implicit column-list /// used by an INSERT statement that lacks an explicit column-list. /// <![CDATA[</ul>]]> /// </para> /// <para> /// For example, if the following SQL is passed to sqlite3_declare_vtab(): /// </para> /// <para><code> /// CREATE TABLE x(a HIDDEN VARCHAR(12), b INTEGER, c INTEGER Hidden); /// </code></para> /// <para> /// Then the virtual table would be created with two hidden columns, /// and with datatypes of "VARCHAR(12)" and "INTEGER". /// </para> /// <para> /// An example use of hidden columns can be seen in the FTS3 virtual /// table implementation, where every FTS virtual table /// contains an FTS hidden column that is used to pass information from the /// virtual table into FTS auxiliary functions and to the FTS MATCH operator. /// </para> /// <para> /// A virtual table that contains hidden columns can be used like /// a table-valued function in the FROM clause of a SELECT statement. /// The arguments to the table-valued function become constraints on /// the HIDDEN columns of the virtual table. /// </para> /// <para> /// For example, the "generate_series" extension (located in the /// ext/misc/series.c /// file in the source tree) /// implements an eponymous virtual table with the following schema: /// </para> /// <para><code> /// CREATE TABLE generate_series( /// value, /// start HIDDEN, /// stop HIDDEN, /// step HIDDEN /// ); /// </code></para> /// <para> /// The sqlite3_module.xBestIndex method in the implementation of this /// table checks for equality constraints against the HIDDEN columns, and uses /// those as input parameters to determine the range of integer "value" outputs /// to generate. Reasonable defaults are used for any unconstrained columns. /// For example, to list all integers between 5 and 50: /// </para> /// <para><code> /// SELECT value FROM generate_series(5,50); /// </code></para> /// <para> /// The previous query is equivalent to the following: /// </para> /// <para><code> /// SELECT value FROM generate_series WHERE start=5 AND stop=50; /// </code></para> /// <para> /// Arguments on the virtual table name are matched to hidden columns /// in order. The number of arguments can be less than the /// number of hidden columns, in which case the latter hidden columns are /// unconstrained. However, an error results if there are more arguments /// than there are hidden columns in the virtual table. /// </para> /// </summary> /// <param name="pDb"> /// The native database connection handle. /// </param> /// <param name="pAux"> /// The original native pointer value that was provided to the |
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101 102 103 104 105 106 107 108 | ref IntPtr pVtab, ref IntPtr pError ); /////////////////////////////////////////////////////////////////////// /// <summary> /// <para> | > > > > > > | | > | | | | | | | > | | | | | | | | | | < | | | | > | | | | | | | 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 | ref IntPtr pVtab, ref IntPtr pError ); /////////////////////////////////////////////////////////////////////// /// <summary> /// <para><code> /// int (*xConnect)(sqlite3*, void *pAux, /// int argc, char **argv, /// sqlite3_vtab **ppVTab, /// char **pzErr); /// </code></para> /// <para> /// The xConnect method is very similar to xCreate. /// It has the same parameters and constructs a new sqlite3_vtab structure /// just like xCreate. /// And it must also call sqlite3_declare_vtab() like xCreate. /// </para> /// <para> /// The difference is that xConnect is called to establish a new /// connection to an existing virtual table whereas xCreate is called /// to create a new virtual table from scratch. /// </para> /// <para> /// The xCreate and xConnect methods are only different when the /// virtual table has some kind of backing store that must be initialized /// the first time the virtual table is created. The xCreate method creates /// and initializes the backing store. The xConnect method just connects /// to an existing backing store. When xCreate and xConnect are the same, /// the table is an eponymous virtual table. /// </para> /// <para> /// As an example, consider a virtual table implementation that /// provides read-only access to existing comma-separated-value (CSV) /// files on disk. There is no backing store that needs to be created /// or initialized for such a virtual table (since the CSV files already /// exist on disk) so the xCreate and xConnect methods will be identical /// for that module. /// </para> /// <para> /// Another example is a virtual table that implements a full-text index. /// The xCreate method must create and initialize data structures to hold /// the dictionary and posting lists for that index. The xConnect method, /// on the other hand, only has to locate and use an existing dictionary /// and posting lists that were created by a prior xCreate call. /// </para> /// <para> /// The xConnect method must return SQLITE_OK if it is successful /// in creating the new virtual table, or SQLITE_ERROR if it is not /// successful. If not successful, the sqlite3_vtab structure must not be /// allocated. An error message may optionally be returned in *pzErr if /// unsuccessful. /// Space to hold the error message string must be allocated using /// an SQLite memory allocation function like /// sqlite3_malloc() or sqlite3_mprintf() as the SQLite core will /// attempt to free the space using sqlite3_free() after the error has /// been reported up to the application. /// </para> /// <para> /// The xConnect method is required for every virtual table implementation, /// though the xCreate and xConnect pointers of the sqlite3_module object /// may point to the same function if the virtual table does not need to /// initialize backing store. /// </para> /// </summary> /// <param name="pDb"> /// The native database connection handle. /// </param> /// <param name="pAux"> /// The original native pointer value that was provided to the |
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192 193 194 195 196 197 198 | ref IntPtr pError ); /////////////////////////////////////////////////////////////////////// /// <summary> /// <para> | | | | | | | | | | | | < | | | | | | < | | | < | | < | | | | | | < | | < | | | < | < | | > > > > | | > > > > > > > > > | | | | | | | > | | | | | | | | | | | | | | | | | | | | | | | | | | < | | | | < < < < | | | | | | | | | | | | | | | | | | > | | | | | | < | | | | | | | | > | | | | | | | | | | | | | | | | | | | < < < | | | | | | | | | | | | | | | | | | | | | | | > > > > > > > > > > > > | | | > | | > | | | | < | | | | | | > > > | | | | > | | | | < > > > | | | | | < | | | < > > > | | | | | | > | | | | | | < > > > | > | | | | < > > > > | | | | | > | | | | | | | | > | | | | < | 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 | ref IntPtr pError ); /////////////////////////////////////////////////////////////////////// /// <summary> /// <para> /// SQLite uses the xBestIndex method of a virtual table module to determine /// the best way to access the virtual table. /// The xBestIndex method has a prototype like this: /// </para> /// <para><code> /// int (*xBestIndex)(sqlite3_vtab *pVTab, sqlite3_index_info*); /// </code></para> /// <para> /// The SQLite core communicates with the xBestIndex method by filling /// in certain fields of the sqlite3_index_info structure and passing a /// pointer to that structure into xBestIndex as the second parameter. /// The xBestIndex method fills out other fields of this structure which /// forms the reply. The sqlite3_index_info structure looks like this: /// </para> /// <para><code> /// struct sqlite3_index_info { /// /* Inputs */ /// const int nConstraint; /* Number of entries in aConstraint */ /// const struct sqlite3_index_constraint { /// int iColumn; /* Column on left-hand side of constraint */ /// unsigned char op; /* Constraint operator */ /// unsigned char usable; /* True if this constraint is usable */ /// int iTermOffset; /* Used internally - xBestIndex should ignore */ /// } *const aConstraint; /* Table of WHERE clause constraints */ /// const int nOrderBy; /* Number of terms in the ORDER BY clause */ /// const struct sqlite3_index_orderby { /// int iColumn; /* Column number */ /// unsigned char desc; /* True for DESC. False for ASC. */ /// } *const aOrderBy; /* The ORDER BY clause */ /// /* Outputs */ /// struct sqlite3_index_constraint_usage { /// int argvIndex; /* if >0, constraint is part of argv to xFilter */ /// unsigned char omit; /* Do not code a test for this constraint */ /// } *const aConstraintUsage; /// int idxNum; /* Number used to identify the index */ /// char *idxStr; /* String, possibly obtained from sqlite3_malloc */ /// int needToFreeIdxStr; /* Free idxStr using sqlite3_free() if true */ /// int orderByConsumed; /* True if output is already ordered */ /// double estimatedCost; /* Estimated cost of using this index */ /// <![CDATA[<b>]]>/* Fields below are only available in SQLite 3.8.2 and later */<![CDATA[</b>]]> /// sqlite3_int64 estimatedRows; /* Estimated number of rows returned */ /// <![CDATA[<b>]]>/* Fields below are only available in SQLite 3.9.0 and later */<![CDATA[</b>]]> /// int idxFlags; /* Mask of SQLITE_INDEX_SCAN_* flags */ /// }; /// </code></para> /// <para> /// Please note the warnings on the "estimatedRows" and "idxFlags" field. /// These fields were added with SQLite versions 3.8.2 and 3.9.0, respectively. /// Any extension that reads or writes these fields must first check that the /// version of the SQLite library in use is greater than or equal to 3.8.2 or /// 3.9.0 - perhaps using a call to sqlite3_version(). The result of attempting /// to access these fields in an sqlite3_index_info structure created by an /// older version of SQLite are undefined. /// </para> /// <para> /// In addition, there are some defined constants: /// </para> /// <para><code> /// #define SQLITE_INDEX_CONSTRAINT_EQ 2 /// #define SQLITE_INDEX_CONSTRAINT_GT 4 /// #define SQLITE_INDEX_CONSTRAINT_LE 8 /// #define SQLITE_INDEX_CONSTRAINT_LT 16 /// #define SQLITE_INDEX_CONSTRAINT_GE 32 /// #define SQLITE_INDEX_CONSTRAINT_MATCH 64 /// #define SQLITE_INDEX_SCAN_UNIQUE 1 /* Scan visits at most 1 row */ /// </code></para> /// <para> /// The SQLite core calls the xBestIndex method when it is compiling a query /// that involves a virtual table. In other words, SQLite calls this method /// when it is running sqlite3_prepare() or the equivalent. /// By calling this method, the /// SQLite core is saying to the virtual table that it needs to access /// some subset of the rows in the virtual table and it wants to know the /// most efficient way to do that access. The xBestIndex method replies /// with information that the SQLite core can then use to conduct an /// efficient search of the virtual table. /// </para> /// <para> /// While compiling a single SQL query, the SQLite core might call /// xBestIndex multiple times with different settings in sqlite3_index_info. /// The SQLite core will then select the combination that appears to /// give the best performance. /// </para> /// <para> /// Before calling this method, the SQLite core initializes an instance /// of the sqlite3_index_info structure with information about the /// query that it is currently trying to process. This information /// derives mainly from the WHERE clause and ORDER BY or GROUP BY clauses /// of the query, but also from any ON or USING clauses if the query is a /// join. The information that the SQLite core provides to the xBestIndex /// method is held in the part of the structure that is marked as "Inputs". /// The "Outputs" section is initialized to zero. /// </para> /// <para> /// The information in the sqlite3_index_info structure is ephemeral /// and may be overwritten or deallocated as soon as the xBestIndex method /// returns. If the xBestIndex method needs to remember any part of the /// sqlite3_index_info structure, it should make a copy. Care must be /// take to store the copy in a place where it will be deallocated, such /// as in the idxStr field with needToFreeIdxStr set to 1. /// </para> /// <para> /// Note that xBestIndex will always be called before xFilter, since /// the idxNum and idxStr outputs from xBestIndex are required inputs to /// xFilter. However, there is no guarantee that xFilter will be called /// following a successful xBestIndex. /// </para> /// <para> /// The xBestIndex method is required for every virtual table implementation. /// </para> /// <para> /// The main thing that the SQLite core is trying to communicate to /// the virtual table is the constraints that are available to limit /// the number of rows that need to be searched. The aConstraint[] array /// contains one entry for each constraint. There will be exactly /// nConstraint entries in that array. /// </para> /// <para> /// Each constraint will correspond to a term in the WHERE clause /// or in a USING or ON clause that is of the form /// </para> /// <para><code> /// column OP EXPR /// </code></para> /// <para> /// Where "column" is a column in the virtual table, OP is an operator /// like "=" or "<", and EXPR is an arbitrary expression. So, for example, /// if the WHERE clause contained a term like this: /// </para> /// <para><code> /// a = 5 /// </code></para> /// <para> /// Then one of the constraints would be on the "a" column with /// operator "=" and an expression of "5". Constraints need not have a /// literal representation of the WHERE clause. The query optimizer might /// make transformations to the /// WHERE clause in order to extract as many constraints /// as it can. So, for example, if the WHERE clause contained something /// like this: /// </para> /// <para><code> /// x BETWEEN 10 AND 100 AND 999>y /// </code></para> /// <para> /// The query optimizer might translate this into three separate constraints: /// </para> /// <para><code> /// x >= 10 /// x <= 100 /// y < 999 /// </code></para> /// <para> /// For each constraint, the aConstraint[].iColumn field indicates which /// column appears on the left-hand side of the constraint. /// The first column of the virtual table is column 0. /// The rowid of the virtual table is column -1. /// The aConstraint[].op field indicates which operator is used. /// The SQLITE_INDEX_CONSTRAINT_* constants map integer constants /// into operator values. /// Columns occur in the order they were defined by the call to /// sqlite3_declare_vtab() in the xCreate or xConnect method. /// Hidden columns are counted when determining the column index. /// </para> /// <para> /// The aConstraint[] array contains information about all constraints /// that apply to the virtual table. But some of the constraints might /// not be usable because of the way tables are ordered in a join. /// The xBestIndex method must therefore only consider constraints /// that have an aConstraint[].usable flag which is true. /// </para> /// <para> /// In addition to WHERE clause constraints, the SQLite core also /// tells the xBestIndex method about the ORDER BY clause. /// (In an aggregate query, the SQLite core might put in GROUP BY clause /// information in place of the ORDER BY clause information, but this fact /// should not make any difference to the xBestIndex method.) /// If all terms of the ORDER BY clause are columns in the virtual table, /// then nOrderBy will be the number of terms in the ORDER BY clause /// and the aOrderBy[] array will identify the column for each term /// in the order by clause and whether or not that column is ASC or DESC. /// </para> /// <para> /// Given all of the information above, the job of the xBestIndex /// method it to figure out the best way to search the virtual table. /// </para> /// <para> /// The xBestIndex method fills the idxNum and idxStr fields with /// information that communicates an indexing strategy to the xFilter /// method. The information in idxNum and idxStr is arbitrary as far /// as the SQLite core is concerned. The SQLite core just copies the /// information through to the xFilter method. Any desired meaning can /// be assigned to idxNum and idxStr as long as xBestIndex and xFilter /// agree on what that meaning is. /// </para> /// <para> /// The idxStr value may be a string obtained from an SQLite /// memory allocation function such as sqlite3_mprintf(). /// If this is the case, then the needToFreeIdxStr flag must be set to /// true so that the SQLite core will know to call sqlite3_free() on /// that string when it has finished with it, and thus avoid a memory leak. /// </para> /// <para> /// If the virtual table will output rows in the order specified by /// the ORDER BY clause, then the orderByConsumed flag may be set to /// true. If the output is not automatically in the correct order /// then orderByConsumed must be left in its default false setting. /// This will indicate to the SQLite core that it will need to do a /// separate sorting pass over the data after it comes out of the virtual table. /// </para> /// <para> /// The estimatedCost field should be set to the estimated number /// of disk access operations required to execute this query against /// the virtual table. The SQLite core will often call xBestIndex /// multiple times with different constraints, obtain multiple cost /// estimates, then choose the query plan that gives the lowest estimate. /// </para> /// <para> /// If the current version of SQLite is 3.8.2 or greater, the estimatedRows /// field may be set to an estimate of the number of rows returned by the /// proposed query plan. If this value is not explicitly set, the default /// estimate of 25 rows is used. /// </para> /// <para> /// If the current version of SQLite is 3.9.0 or greater, the idxFlags field /// may be set to SQLITE_INDEX_SCAN_UNIQUE to indicate that the virtual table /// will return only zero or one rows given the input constraints. Additional /// bits of the idxFlags field might be understood in later versions of SQLite. /// </para> /// <para> /// The aConstraintUsage[] array contains one element for each of /// the nConstraint constraints in the inputs section of the /// sqlite3_index_info structure. /// The aConstraintUsage[] array is used by xBestIndex to tell the /// core how it is using the constraints. /// </para> /// <para> /// The xBestIndex method may set aConstraintUsage[].argvIndex /// entries to values greater than zero. /// Exactly one entry should be set to 1, another to 2, another to 3, /// and so forth up to as many or as few as the xBestIndex method wants. /// The EXPR of the corresponding constraints will then be passed /// in as the argv[] parameters to xFilter. /// </para> /// <para> /// For example, if the aConstraint[3].argvIndex is set to 1, then /// when xFilter is called, the argv[0] passed to xFilter will have /// the EXPR value of the aConstraint[3] constraint. /// </para> /// <para> /// By default, the SQLite core double checks all constraints on /// each row of the virtual table that it receives. If such a check /// is redundant, the xBestFilter method can suppress that double-check by /// setting aConstraintUsage[].omit. /// </para> /// </summary> /// <param name="pVtab"> /// The native pointer to the sqlite3_vtab derived structure. /// </param> /// <param name="pIndex"> /// The native pointer to the sqlite3_index_info structure. /// </param> /// <returns> /// A standard SQLite return code. /// </returns> SQLiteErrorCode xBestIndex( IntPtr pVtab, IntPtr pIndex ); /////////////////////////////////////////////////////////////////////// /// <summary> /// <para><code> /// int (*xDisconnect)(sqlite3_vtab *pVTab); /// </code></para> /// <para> /// This method releases a connection to a virtual table. /// Only the sqlite3_vtab object is destroyed. /// The virtual table is not destroyed and any backing store /// associated with the virtual table persists. /// </para> /// This method undoes the work of xConnect. /// <para> /// This method is a destructor for a connection to the virtual table. /// Contrast this method with xDestroy. The xDestroy is a destructor /// for the entire virtual table. /// </para> /// <para> /// The xDisconnect method is required for every virtual table implementation, /// though it is acceptable for the xDisconnect and xDestroy methods to be /// the same function if that makes sense for the particular virtual table. /// </para> /// </summary> /// <param name="pVtab"> /// The native pointer to the sqlite3_vtab derived structure. /// </param> /// <returns> /// A standard SQLite return code. /// </returns> SQLiteErrorCode xDisconnect( IntPtr pVtab ); /////////////////////////////////////////////////////////////////////// /// <summary> /// <para><code> /// int (*xDestroy)(sqlite3_vtab *pVTab); /// </code></para> /// <para> /// This method releases a connection to a virtual table, just like /// the xDisconnect method, and it also destroys the underlying /// table implementation. This method undoes the work of xCreate. /// </para> /// <para> /// The xDisconnect method is called whenever a database connection /// that uses a virtual table is closed. The xDestroy method is only /// called when a DROP TABLE statement is executed against the virtual table. /// </para> /// <para> /// The xDestroy method is required for every virtual table implementation, /// though it is acceptable for the xDisconnect and xDestroy methods to be /// the same function if that makes sense for the particular virtual table. /// </para> /// </summary> /// <param name="pVtab"> /// The native pointer to the sqlite3_vtab derived structure. /// </param> /// <returns> /// A standard SQLite return code. /// </returns> SQLiteErrorCode xDestroy( IntPtr pVtab ); /////////////////////////////////////////////////////////////////////// /// <summary> /// <para><code> /// int (*xOpen)(sqlite3_vtab *pVTab, sqlite3_vtab_cursor **ppCursor); /// </code></para> /// <para> /// The xOpen method creates a new cursor used for accessing (read and/or /// writing) a virtual table. A successful invocation of this method /// will allocate the memory for the sqlite3_vtab_cursor (or a subclass), /// initialize the new object, and make *ppCursor point to the new object. /// The successful call then returns SQLITE_OK. /// </para> /// <para> /// For every successful call to this method, the SQLite core will /// later invoke the xClose method to destroy /// the allocated cursor. /// </para> /// <para> /// The xOpen method need not initialize the pVtab field of the /// sqlite3_vtab_cursor structure. The SQLite core will take care /// of that chore automatically. /// </para> /// <para> /// A virtual table implementation must be able to support an arbitrary /// number of simultaneously open cursors. /// </para> /// <para> /// When initially opened, the cursor is in an undefined state. /// The SQLite core will invoke the xFilter method /// on the cursor prior to any attempt to position or read from the cursor. /// </para> /// <para> /// The xOpen method is required for every virtual table implementation. /// </para> /// </summary> /// <param name="pVtab"> /// The native pointer to the sqlite3_vtab derived structure. /// </param> /// <param name="pCursor"> /// Upon success, this parameter must be modified to point to the newly /// created native sqlite3_vtab_cursor derived structure. /// </param> /// <returns> /// A standard SQLite return code. /// </returns> SQLiteErrorCode xOpen( IntPtr pVtab, ref IntPtr pCursor ); /////////////////////////////////////////////////////////////////////// /// <summary> /// <para><code> /// int (*xClose)(sqlite3_vtab_cursor*); /// </code></para> /// <para> /// The xClose method closes a cursor previously opened by /// xOpen. /// The SQLite core will always call xClose once for each cursor opened /// using xOpen. /// </para> /// <para> /// This method must release all resources allocated by the /// corresponding xOpen call. The routine will not be called again even if it /// returns an error. The SQLite core will not use the /// sqlite3_vtab_cursor again after it has been closed. /// </para> /// <para> /// The xClose method is required for every virtual table implementation. /// </para> /// </summary> /// <param name="pCursor"> /// The native pointer to the sqlite3_vtab_cursor derived structure. /// </param> /// <returns> /// A standard SQLite return code. /// </returns> SQLiteErrorCode xClose( IntPtr pCursor ); /////////////////////////////////////////////////////////////////////// /// <summary> /// <para><code> /// int (*xFilter)(sqlite3_vtab_cursor*, int idxNum, const char *idxStr, /// int argc, sqlite3_value **argv); /// </code></para> /// <para> /// This method begins a search of a virtual table. /// The first argument is a cursor opened by xOpen. /// The next two arguments define a particular search index previously /// chosen by xBestIndex. The specific meanings of idxNum and idxStr /// are unimportant as long as xFilter and xBestIndex agree on what /// that meaning is. /// </para> /// <para> /// The xBestIndex function may have requested the values of /// certain expressions using the aConstraintUsage[].argvIndex values /// of the sqlite3_index_info structure. /// Those values are passed to xFilter using the argc and argv parameters. /// </para> /// <para> /// If the virtual table contains one or more rows that match the /// search criteria, then the cursor must be left point at the first row. /// Subsequent calls to xEof must return false (zero). /// If there are no rows match, then the cursor must be left in a state /// that will cause the xEof to return true (non-zero). /// The SQLite engine will use /// the xColumn and xRowid methods to access that row content. /// The xNext method will be used to advance to the next row. /// </para> /// <para> /// This method must return SQLITE_OK if successful, or an sqlite /// error code if an error occurs. /// </para> /// <para> /// The xFilter method is required for every virtual table implementation. /// </para> /// </summary> /// <param name="pCursor"> /// The native pointer to the sqlite3_vtab_cursor derived structure. /// </param> /// <param name="idxNum"> /// Number used to help identify the selected index. |
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655 656 657 658 659 660 661 662 | int argc, IntPtr argv ); /////////////////////////////////////////////////////////////////////// /// <summary> /// <para> | > > > | | | | | | | | | | < > > > | | | | > > > | | > | | | > | | | | | | | | | | > | | | | | | < | < | 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 | int argc, IntPtr argv ); /////////////////////////////////////////////////////////////////////// /// <summary> /// <para><code> /// int (*xNext)(sqlite3_vtab_cursor*); /// </code></para> /// <para> /// The xNext method advances a virtual table cursor /// to the next row of a result set initiated by xFilter. /// If the cursor is already pointing at the last row when this /// routine is called, then the cursor no longer points to valid /// data and a subsequent call to the xEof method must return true (non-zero). /// If the cursor is successfully advanced to another row of content, then /// subsequent calls to xEof must return false (zero). /// </para> /// <para> /// This method must return SQLITE_OK if successful, or an sqlite /// error code if an error occurs. /// </para> /// <para> /// The xNext method is required for every virtual table implementation. /// </para> /// </summary> /// <param name="pCursor"> /// The native pointer to the sqlite3_vtab_cursor derived structure. /// </param> /// <returns> /// A standard SQLite return code. /// </returns> SQLiteErrorCode xNext( IntPtr pCursor ); /////////////////////////////////////////////////////////////////////// /// <summary> /// <para><code> /// int (*xEof)(sqlite3_vtab_cursor*); /// </code></para> /// <para> /// The xEof method must return false (zero) if the specified cursor /// currently points to a valid row of data, or true (non-zero) otherwise. /// This method is called by the SQL engine immediately after each /// xFilter and xNext invocation. /// </para> /// <para> /// The xEof method is required for every virtual table implementation. /// </para> /// </summary> /// <param name="pCursor"> /// The native pointer to the sqlite3_vtab_cursor derived structure. /// </param> /// <returns> /// Non-zero if no more rows are available; zero otherwise. /// </returns> int xEof( IntPtr pCursor ); /////////////////////////////////////////////////////////////////////// /// <summary> /// <para><code> /// int (*xColumn)(sqlite3_vtab_cursor*, sqlite3_context*, int N); /// </code></para> /// <para> /// The SQLite core invokes this method in order to find the value for /// the N-th column of the current row. N is zero-based so the first column /// is numbered 0. /// The xColumn method may return its result back to SQLite using one of the /// following interface: /// </para> /// <para> /// <![CDATA[<ul>]]> /// <![CDATA[<li>]]> sqlite3_result_blob() /// <![CDATA[<li>]]> sqlite3_result_double() /// <![CDATA[<li>]]> sqlite3_result_int() /// <![CDATA[<li>]]> sqlite3_result_int64() /// <![CDATA[<li>]]> sqlite3_result_null() /// <![CDATA[<li>]]> sqlite3_result_text() /// <![CDATA[<li>]]> sqlite3_result_text16() /// <![CDATA[<li>]]> sqlite3_result_text16le() /// <![CDATA[<li>]]> sqlite3_result_text16be() /// <![CDATA[<li>]]> sqlite3_result_zeroblob() /// <![CDATA[</ul>]]> /// </para> /// <para> /// If the xColumn method implementation calls none of the functions above, /// then the value of the column defaults to an SQL NULL. /// </para> /// <para> /// To raise an error, the xColumn method should use one of the result_text() /// methods to set the error message text, then return an appropriate /// error code. The xColumn method must return SQLITE_OK on success. /// </para> /// <para> /// The xColumn method is required for every virtual table implementation. /// </para> /// </summary> /// <param name="pCursor"> /// The native pointer to the sqlite3_vtab_cursor derived structure. /// </param> /// <param name="pContext"> /// The native pointer to the sqlite3_context structure to be used |
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766 767 768 769 770 771 772 773 774 | IntPtr pContext, int index ); /////////////////////////////////////////////////////////////////////// /// <summary> /// <para> /// A successful invocation of this method will cause *pRowid to be | > > > | > | | | < > > > > > > > > | | | | < | | > | | | | | | | | | < | | | | | | | | | | | < < < < < < < < < < | | > > > > | | | < < < < | < < | | < < < < < < < > | | | < | < | | > > | | | | < | | | | | | | | | < | | | | 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 | IntPtr pContext, int index ); /////////////////////////////////////////////////////////////////////// /// <summary> /// <para><code> /// int (*xRowid)(sqlite3_vtab_cursor *pCur, sqlite_int64 *pRowid); /// </code></para> /// <para> /// A successful invocation of this method will cause *pRowid to be /// filled with the rowid of row that the /// virtual table cursor pCur is currently pointing at. /// This method returns SQLITE_OK on success. /// It returns an appropriate error code on failure. /// </para> /// <para> /// The xRowid method is required for every virtual table implementation. /// </para> /// </summary> /// <param name="pCursor"> /// The native pointer to the sqlite3_vtab_cursor derived structure. /// </param> /// <param name="rowId"> /// Upon success, this parameter must be modified to contain the unique /// integer row identifier for the current row for the specified cursor. /// </param> /// <returns> /// A standard SQLite return code. /// </returns> SQLiteErrorCode xRowId( IntPtr pCursor, ref long rowId ); /////////////////////////////////////////////////////////////////////// /// <summary> /// <para><code> /// int (*xUpdate)( /// sqlite3_vtab *pVTab, /// int argc, /// sqlite3_value **argv, /// sqlite_int64 *pRowid /// ); /// </code></para> /// <para> /// All changes to a virtual table are made using the xUpdate method. /// This one method can be used to insert, delete, or update. /// </para> /// <para> /// The argc parameter specifies the number of entries in the argv array. /// The value of argc will be 1 for a pure delete operation or N+2 for an insert /// or replace or update where N is the number of columns in the table. /// In the previous sentence, N includes any hidden columns. /// </para> /// <para> /// Every argv entry will have a non-NULL value in C but may contain the /// SQL value NULL. In other words, it is always true that /// <![CDATA[<tt>]]>argv[i]!=0<![CDATA[</tt>]]> for <![CDATA[<b>]]>i<![CDATA[</b>]]> between 0 and <![CDATA[<tt>]]>argc-1<![CDATA[</tt>]]>. /// However, it might be the case that /// <![CDATA[<tt>]]>sqlite3_value_type(argv[i])==SQLITE_NULL<![CDATA[</tt>]]>. /// </para> /// <para> /// The argv[0] parameter is the rowid of a row in the virtual table /// to be deleted. If argv[0] is an SQL NULL, then no deletion occurs. /// </para> /// <para> /// The argv[1] parameter is the rowid of a new row to be inserted /// into the virtual table. If argv[1] is an SQL NULL, then the implementation /// must choose a rowid for the newly inserted row. Subsequent argv[] /// entries contain values of the columns of the virtual table, in the /// order that the columns were declared. The number of columns will /// match the table declaration that the xConnect or xCreate method made /// using the sqlite3_declare_vtab() call. All hidden columns are included. /// </para> /// <para> /// When doing an insert without a rowid (argc>1, argv[1] is an SQL NULL), the /// implementation must set *pRowid to the rowid of the newly inserted row; /// this will become the value returned by the sqlite3_last_insert_rowid() /// function. Setting this value in all the other cases is a harmless no-op; /// the SQLite engine ignores the *pRowid return value if argc==1 or /// argv[1] is not an SQL NULL. /// </para> /// <para> /// Each call to xUpdate will fall into one of cases shown below. /// Not that references to <![CDATA[<b>]]>argv[i]<![CDATA[</b>]]> mean the SQL value /// held within the argv[i] object, not the argv[i] /// object itself. /// </para> /// <para><code> /// <![CDATA[<dl>]]> /// <![CDATA[<dt>]]><![CDATA[<b>]]>argc = 1<![CDATA[</b>]]> /// <![CDATA[<dd>]]>The single row with rowid equal to argv[0] is deleted. No insert occurs. /// <![CDATA[<dt>]]><![CDATA[<b>]]>argc > 1 <![CDATA[<br>]]> argv[0] = NULL<![CDATA[</b>]]> /// <![CDATA[<dd>]]>A new row is inserted with a rowid argv[1] and column values in /// argv[2] and following. If argv[1] is an SQL NULL, /// the a new unique rowid is generated automatically. /// <![CDATA[<dt>]]><![CDATA[<b>]]>argc > 1 <![CDATA[<br>]]> argv[0] ≠ NULL <![CDATA[<br>]]> argv[0] = argv[1]<![CDATA[</b>]]> /// <![CDATA[<dd>]]>The row with rowid argv[0] is updated with new values /// in argv[2] and following parameters. /// <![CDATA[<dt>]]><![CDATA[<b>]]>argc > 1 <![CDATA[<br>]]> argv[0] ≠ NULL <![CDATA[<br>]]> argv[0] ≠ argv[1]<![CDATA[</b>]]> /// <![CDATA[<dd>]]> The row with rowid argv[0] is updated with rowid argv[1] /// and new values in argv[2] and following parameters. This will occur /// when an SQL statement updates a rowid, as in the statement: /// <para><code> /// UPDATE table SET rowid=rowid+1 WHERE ...; /// </code></para> /// <![CDATA[</dl>]]> /// </code></para> /// <para> /// The xUpdate method must return SQLITE_OK if and only if it is /// successful. If a failure occurs, the xUpdate must return an appropriate /// error code. On a failure, the pVTab->zErrMsg element may optionally /// be replaced with error message text stored in memory allocated from SQLite /// using functions such as sqlite3_mprintf() or sqlite3_malloc(). /// </para> /// <para> /// If the xUpdate method violates some constraint of the virtual table /// (including, but not limited to, attempting to store a value of the wrong /// datatype, attempting to store a value that is too /// large or too small, or attempting to change a read-only value) then the /// xUpdate must fail with an appropriate error code. /// </para> /// <para> /// There might be one or more sqlite3_vtab_cursor objects open and in use /// on the virtual table instance and perhaps even on the row of the virtual /// table when the xUpdate method is invoked. The implementation of /// xUpdate must be prepared for attempts to delete or modify rows of the table /// out from other existing cursors. If the virtual table cannot accommodate /// such changes, the xUpdate method must return an error code. /// </para> /// <para> /// The xUpdate method is optional. /// If the xUpdate pointer in the sqlite3_module for a virtual table /// is a NULL pointer, then the virtual table is read-only. /// </para> /// </summary> /// <param name="pVtab"> /// The native pointer to the sqlite3_vtab derived structure. /// </param> /// <param name="argc"> /// The number of new or modified column values contained in |
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936 937 938 939 940 941 942 943 | IntPtr argv, ref long rowId ); /////////////////////////////////////////////////////////////////////// /// <summary> /// <para> | > > > | | > | | | > | | | < > > > > | | | | > > > | | | > > > | | | > > > > > > > > > | | | > > > > > > > > > | > > > > > | | > > | 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184 1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217 1218 1219 1220 1221 1222 1223 1224 1225 1226 1227 1228 1229 1230 1231 1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 | IntPtr argv, ref long rowId ); /////////////////////////////////////////////////////////////////////// /// <summary> /// <para><code> /// int (*xBegin)(sqlite3_vtab *pVTab); /// </code></para> /// <para> /// This method begins a transaction on a virtual table. /// This is method is optional. The xBegin pointer of sqlite3_module /// may be NULL. /// </para> /// <para> /// This method is always followed by one call to either the /// xCommit or xRollback method. Virtual table transactions do /// not nest, so the xBegin method will not be invoked more than once /// on a single virtual table /// without an intervening call to either xCommit or xRollback. /// Multiple calls to other methods can and likely will occur in between /// the xBegin and the corresponding xCommit or xRollback. /// </para> /// </summary> /// <param name="pVtab"> /// The native pointer to the sqlite3_vtab derived structure. /// </param> /// <returns> /// A standard SQLite return code. /// </returns> SQLiteErrorCode xBegin( IntPtr pVtab ); /////////////////////////////////////////////////////////////////////// /// <summary> /// <para><code> /// int (*xSync)(sqlite3_vtab *pVTab); /// </code></para> /// <para> /// This method signals the start of a two-phase commit on a virtual /// table. /// This is method is optional. The xSync pointer of sqlite3_module /// may be NULL. /// </para> /// <para> /// This method is only invoked after call to the xBegin method and /// prior to an xCommit or xRollback. In order to implement two-phase /// commit, the xSync method on all virtual tables is invoked prior to /// invoking the xCommit method on any virtual table. If any of the /// xSync methods fail, the entire transaction is rolled back. /// </para> /// </summary> /// <param name="pVtab"> /// The native pointer to the sqlite3_vtab derived structure. /// </param> /// <returns> /// A standard SQLite return code. /// </returns> SQLiteErrorCode xSync( IntPtr pVtab ); /////////////////////////////////////////////////////////////////////// /// <summary> /// <para><code> /// int (*xCommit)(sqlite3_vtab *pVTab); /// </code></para> /// <para> /// This method causes a virtual table transaction to commit. /// This is method is optional. The xCommit pointer of sqlite3_module /// may be NULL. /// </para> /// <para> /// A call to this method always follows a prior call to xBegin and /// xSync. /// </para> /// </summary> /// <param name="pVtab"> /// The native pointer to the sqlite3_vtab derived structure. /// </param> /// <returns> /// A standard SQLite return code. /// </returns> SQLiteErrorCode xCommit( IntPtr pVtab ); /////////////////////////////////////////////////////////////////////// /// <summary> /// <para><code> /// int (*xRollback)(sqlite3_vtab *pVTab); /// </code></para> /// <para> /// This method causes a virtual table transaction to rollback. /// This is method is optional. The xRollback pointer of sqlite3_module /// may be NULL. /// </para> /// <para> /// A call to this method always follows a prior call to xBegin. /// </para> /// </summary> /// <param name="pVtab"> /// The native pointer to the sqlite3_vtab derived structure. /// </param> /// <returns> /// A standard SQLite return code. /// </returns> SQLiteErrorCode xRollback( IntPtr pVtab ); /////////////////////////////////////////////////////////////////////// /// <summary> /// <para><code> /// int (*xFindFunction)( /// sqlite3_vtab *pVtab, /// int nArg, /// const char *zName, /// void (**pxFunc)(sqlite3_context*,int,sqlite3_value**), /// void **ppArg /// ); /// </code></para> /// <para> /// This method is called during sqlite3_prepare() to give the virtual /// table implementation an opportunity to overload functions. /// This method may be set to NULL in which case no overloading occurs. /// </para> /// <para> /// When a function uses a column from a virtual table as its first /// argument, this method is called to see if the virtual table would /// like to overload the function. The first three parameters are inputs: /// the virtual table, the number of arguments to the function, and the /// name of the function. If no overloading is desired, this method /// returns 0. To overload the function, this method writes the new /// function implementation into *pxFunc and writes user data into *ppArg /// and returns 1. /// </para> /// <para> /// Note that infix functions (LIKE, GLOB, REGEXP, and MATCH) reverse /// the order of their arguments. So "like(A,B)" is equivalent to "B like A". /// For the form "B like A" the B term is considered the first argument /// to the function. But for "like(A,B)" the A term is considered the /// first argument. /// </para> /// <para> /// The function pointer returned by this routine must be valid for /// the lifetime of the sqlite3_vtab object given in the first parameter. /// </para> /// </summary> /// <param name="pVtab"> /// The native pointer to the sqlite3_vtab derived structure. /// </param> /// <param name="nArg"> /// The number of arguments to the function being sought. |
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1077 1078 1079 1080 1081 1082 1083 1084 | ref SQLiteCallback callback, ref IntPtr pClientData ); /////////////////////////////////////////////////////////////////////// /// <summary> /// <para> | > > > | | | | | < > > > > > | | | | | > | | > | | | | < | | | > > > > > | | | | | > | | > | | | | < | | | | 1262 1263 1264 1265 1266 1267 1268 1269 1270 1271 1272 1273 1274 1275 1276 1277 1278 1279 1280 1281 1282 1283 1284 1285 1286 1287 1288 1289 1290 1291 1292 1293 1294 1295 1296 1297 1298 1299 1300 1301 1302 1303 1304 1305 1306 1307 1308 1309 1310 1311 1312 1313 1314 1315 1316 1317 1318 1319 1320 1321 1322 1323 1324 1325 1326 1327 1328 1329 1330 1331 1332 1333 1334 1335 1336 1337 1338 1339 1340 1341 1342 1343 1344 1345 1346 1347 1348 1349 1350 1351 1352 1353 1354 1355 1356 1357 1358 1359 1360 1361 1362 1363 1364 1365 1366 1367 1368 1369 1370 1371 1372 1373 1374 1375 1376 1377 1378 | ref SQLiteCallback callback, ref IntPtr pClientData ); /////////////////////////////////////////////////////////////////////// /// <summary> /// <para><code> /// int (*xRename)(sqlite3_vtab *pVtab, const char *zNew); /// </code></para> /// <para> /// This method provides notification that the virtual table implementation /// that the virtual table will be given a new name. /// If this method returns SQLITE_OK then SQLite renames the table. /// If this method returns an error code then the renaming is prevented. /// </para> /// <para> /// The xRename method is required for every virtual table implementation. /// </para> /// </summary> /// <param name="pVtab"> /// The native pointer to the sqlite3_vtab derived structure. /// </param> /// <param name="zNew"> /// The native pointer to the UTF-8 encoded string containing the new /// name for the virtual table. /// </param> /// <returns> /// A standard SQLite return code. /// </returns> SQLiteErrorCode xRename( IntPtr pVtab, IntPtr zNew ); /////////////////////////////////////////////////////////////////////// /// <summary> /// <para><code> /// int (*xSavepoint)(sqlite3_vtab *pVtab, int); /// int (*xRelease)(sqlite3_vtab *pVtab, int); /// int (*xRollbackTo)(sqlite3_vtab *pVtab, int); /// </code></para> /// <para> /// These methods provide the virtual table implementation an opportunity to /// implement nested transactions. They are always optional and will only be /// called in SQLite version 3.7.7 and later. /// </para> /// <para> /// When xSavepoint(X,N) is invoked, that is a signal to the virtual table X /// that it should save its current state as savepoint N. /// A subsequent call /// to xRollbackTo(X,R) means that the state of the virtual table should return /// to what it was when xSavepoint(X,R) was last called. /// The call /// to xRollbackTo(X,R) will invalidate all savepoints with N>R; none of the /// invalided savepoints will be rolled back or released without first /// being reinitialized by a call to xSavepoint(). /// A call to xRelease(X,M) invalidates all savepoints where N>=M. /// </para> /// <para> /// None of the xSavepoint(), xRelease(), or xRollbackTo() methods will ever /// be called except in between calls to xBegin() and /// either xCommit() or xRollback(). /// </para> /// </summary> /// <param name="pVtab"> /// The native pointer to the sqlite3_vtab derived structure. /// </param> /// <param name="iSavepoint"> /// This is an integer identifier under which the the current state of /// the virtual table should be saved. /// </param> /// <returns> /// A standard SQLite return code. /// </returns> SQLiteErrorCode xSavepoint( IntPtr pVtab, int iSavepoint ); /////////////////////////////////////////////////////////////////////// /// <summary> /// <para><code> /// int (*xSavepoint)(sqlite3_vtab *pVtab, int); /// int (*xRelease)(sqlite3_vtab *pVtab, int); /// int (*xRollbackTo)(sqlite3_vtab *pVtab, int); /// </code></para> /// <para> /// These methods provide the virtual table implementation an opportunity to /// implement nested transactions. They are always optional and will only be /// called in SQLite version 3.7.7 and later. /// </para> /// <para> /// When xSavepoint(X,N) is invoked, that is a signal to the virtual table X /// that it should save its current state as savepoint N. /// A subsequent call /// to xRollbackTo(X,R) means that the state of the virtual table should return /// to what it was when xSavepoint(X,R) was last called. /// The call /// to xRollbackTo(X,R) will invalidate all savepoints with N>R; none of the /// invalided savepoints will be rolled back or released without first /// being reinitialized by a call to xSavepoint(). /// A call to xRelease(X,M) invalidates all savepoints where N>=M. /// </para> /// <para> /// None of the xSavepoint(), xRelease(), or xRollbackTo() methods will ever /// be called except in between calls to xBegin() and /// either xCommit() or xRollback(). /// </para> /// </summary> /// <param name="pVtab"> /// The native pointer to the sqlite3_vtab derived structure. /// </param> /// <param name="iSavepoint"> /// This is an integer used to indicate that any saved states with an |
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1187 1188 1189 1190 1191 1192 1193 1194 | IntPtr pVtab, int iSavepoint ); /////////////////////////////////////////////////////////////////////// /// <summary> /// <para> | > > > > > | | | | | > | | > | | | | < | | | < | 1386 1387 1388 1389 1390 1391 1392 1393 1394 1395 1396 1397 1398 1399 1400 1401 1402 1403 1404 1405 1406 1407 1408 1409 1410 1411 1412 1413 1414 1415 1416 1417 1418 1419 1420 1421 1422 1423 1424 1425 1426 1427 1428 1429 1430 1431 1432 1433 1434 1435 1436 1437 1438 1439 | IntPtr pVtab, int iSavepoint ); /////////////////////////////////////////////////////////////////////// /// <summary> /// <para><code> /// int (*xSavepoint)(sqlite3_vtab *pVtab, int); /// int (*xRelease)(sqlite3_vtab *pVtab, int); /// int (*xRollbackTo)(sqlite3_vtab *pVtab, int); /// </code></para> /// <para> /// These methods provide the virtual table implementation an opportunity to /// implement nested transactions. They are always optional and will only be /// called in SQLite version 3.7.7 and later. /// </para> /// <para> /// When xSavepoint(X,N) is invoked, that is a signal to the virtual table X /// that it should save its current state as savepoint N. /// A subsequent call /// to xRollbackTo(X,R) means that the state of the virtual table should return /// to what it was when xSavepoint(X,R) was last called. /// The call /// to xRollbackTo(X,R) will invalidate all savepoints with N>R; none of the /// invalided savepoints will be rolled back or released without first /// being reinitialized by a call to xSavepoint(). /// A call to xRelease(X,M) invalidates all savepoints where N>=M. /// </para> /// <para> /// None of the xSavepoint(), xRelease(), or xRollbackTo() methods will ever /// be called except in between calls to xBegin() and /// either xCommit() or xRollback(). /// </para> /// </summary> /// <param name="pVtab"> /// The native pointer to the sqlite3_vtab derived structure. /// </param> /// <param name="iSavepoint"> /// This is an integer identifier used to specify a specific saved /// state for the virtual table for it to restore itself back to, which /// should also have the effect of deleting all saved states with an /// integer identifier greater than this one. /// </param> /// <returns> /// A standard SQLite return code. /// </returns> SQLiteErrorCode xRollbackTo( IntPtr pVtab, int iSavepoint ); } #endregion } |