System.Data.SQLite
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//---------------------------------------------------------------------
// <copyright file="SymbolTable.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>
//---------------------------------------------------------------------

#if USE_ENTITY_FRAMEWORK_6
namespace System.Data.SQLite.EF6
#else
namespace System.Data.SQLite.Linq
#endif
{
  using System;
  using System.Collections.Generic;

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

  /// <summary>
  /// The symbol table is quite primitive - it is a stack with a new entry for
  /// each scope.  Lookups search from the top of the stack to the bottom, until
  /// an entry is found.
  /// 
  /// The symbols are of the following kinds
  /// <list type="bullet">
  /// <item><see cref="Symbol"/> represents tables (extents/nested selects/unnests)</item>
  /// <item><see cref="JoinSymbol"/> represents Join nodes</item>
  /// <item><see cref="Symbol"/> columns.</item>
  /// </list>
  /// 
  /// Symbols represent names <see cref="SqlGenerator.Visit(DbVariableReferenceExpression)"/> to be resolved, 
  /// or things to be renamed.
  /// </summary>
  internal sealed class SymbolTable
  {
    private List<Dictionary<string, Symbol>> symbols = new List<Dictionary<string, Symbol>>();

    internal void EnterScope()
    {
      symbols.Add(new Dictionary<string, Symbol>(StringComparer.OrdinalIgnoreCase));
    }

    internal void ExitScope()
    {
      symbols.RemoveAt(symbols.Count - 1);
    }

    internal void Add(string name, Symbol value)
    {
      symbols[symbols.Count - 1][name] = value;
    }

    internal Symbol Lookup(string name)
    {
      for (int i = symbols.Count - 1; i >= 0; --i)
      {
        if (symbols[i].ContainsKey(name))
        {
          return symbols[i][name];
        }
      }

      return null;
    }
  }
}