System.Data.SQLite
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//---------------------------------------------------------------------
// <copyright file="SqlBuilder.cs" company="Microsoft">
//      Portions of this file copyright (c) Microsoft Corporation
//      and are released under the Microsoft Pulic License.  See
//      http://archive.msdn.microsoft.com/EFSampleProvider/Project/License.aspx
//      or License.txt for details.
//      All rights reserved.
// </copyright>
//---------------------------------------------------------------------

namespace System.Data.SQLite
{
  using System;
  using System.Collections.Generic;
  using System.Diagnostics;

#if USE_ENTITY_FRAMEWORK_6
  using System.Data.Entity.Core.Common.CommandTrees;
#else
  using System.Data.Common.CommandTrees;
#endif

  /// <summary>
  /// This class is like StringBuilder.  While traversing the tree for the first time, 
  /// we do not know all the strings that need to be appended e.g. things that need to be
  /// renamed, nested select statements etc.  So, we use a builder that can collect
  /// all kinds of sql fragments.
  /// </summary>
  internal sealed class SqlBuilder : ISqlFragment
  {
    private List<object> _sqlFragments;
    private List<object> sqlFragments
    {
      get
      {
        if (null == _sqlFragments)
        {
          _sqlFragments = new List<object>();
        }
        return _sqlFragments;
      }
    }


    /// <summary>
    /// Add an object to the list - we do not verify that it is a proper sql fragment
    /// since this is an internal method.
    /// </summary>
    /// <param name="s"></param>
    public void Append(object s)
    {
      Debug.Assert(s != null);
      sqlFragments.Add(s);
    }

    /// <summary>
    /// This is to pretty print the SQL.  The writer <see cref="SqlWriter.Write"/>
    /// needs to know about new lines so that it can add the right amount of 
    /// indentation at the beginning of lines.
    /// </summary>
    public void AppendLine()
    {
      sqlFragments.Add("\r\n");
    }

    /// <summary>
    /// Whether the builder is empty.  This is used by the <see cref="SqlGenerator.Visit(DbProjectExpression)"/>
    /// to determine whether a sql statement can be reused.
    /// </summary>
    public bool IsEmpty
    {
      get { return ((null == _sqlFragments) || (0 == _sqlFragments.Count)); }
    }

    #region ISqlFragment Members

    /// <summary>
    /// We delegate the writing of the fragment to the appropriate type.
    /// </summary>
    /// <param name="writer"></param>
    /// <param name="sqlGenerator"></param>
    public void WriteSql(SqlWriter writer, SqlGenerator sqlGenerator)
    {
      if (null != _sqlFragments)
      {
        foreach (object o in _sqlFragments)
        {
          string str = (o as String);
          if (null != str)
          {
            writer.Write(str);
          }
          else
          {
            ISqlFragment sqlFragment = (o as ISqlFragment);
            if (null != sqlFragment)
            {
              sqlFragment.WriteSql(writer, sqlGenerator);
            }
            else
            {
              throw new InvalidOperationException();
            }
          }
        }
      }
    }

    #endregion
  }
}