mcs/class/referencesource/System.Data.Entity/System/Data/SqlClient/SqlGen/OptionalColumn.cs

   1 //---------------------------------------------------------------------
   2 // <copyright file="OptionalColumn.cs" company="Microsoft">
   3 //      Copyright (c) Microsoft Corporation.  All rights reserved.
   4 // </copyright>
   5 //
   6 // @owner  Microsoft
   7 //---------------------------------------------------------------------
   8
   9 using System;
  10 using System.Collections.Generic;
  11 using System.Diagnostics;
  12
  13 namespace System.Data.SqlClient.SqlGen
  14 {
  15     /// <summary>
  16     /// Represents a column in a select list that should be printed only if it is later used.
  17     /// Such columns get added by <see cref="SqlGenerator.AddDefaultColumns"/>.
  18     /// The SymbolUsageManager associated with the OptionalColumn has the information whether the column
  19     /// has been used based on its symbol.
  20     /// </summary>
  21     internal sealed class OptionalColumn
  22     {
  23         #region Private State
  24         private readonly SymbolUsageManager m_usageManager;
  25
  26         // The SqlBuilder that contains the column building blocks (e.g: "c.X as X1")
  27         private readonly SqlBuilder m_builder = new SqlBuilder();
  28
  29         // The symbol representing the optional column
  30         private readonly Symbol m_symbol;
  31         #endregion
  32
  33         #region Internal Methods
  34         /// <summary>
  35         /// Append to the "fragment" representing this column
  36         /// </summary>
  37         internal void Append(object s)
  38         {
  39             m_builder.Append(s);
  40         }
  41
  42         internal void MarkAsUsed()
  43         {
  44             this.m_usageManager.MarkAsUsed(this.m_symbol);
  45         }
  46         #endregion
  47
  48         #region Constructor
  49         internal OptionalColumn(SymbolUsageManager usageManager, Symbol symbol)
  50         {
  51             this.m_usageManager = usageManager;
  52             this.m_symbol = symbol;
  53         }
  54         #endregion
  55
  56         #region Internal members
  57
  58         /// <summary>
  59         /// Writes that fragment that represents the optional column
  60         /// if the usage manager says it is used.
  61         /// </summary>
  62         /// <param name="writer"></param>
  63         /// <param name="sqlGenerator"></param>
  64         public bool WriteSqlIfUsed(SqlWriter writer, SqlGenerator sqlGenerator, string separator)
  65         {
  66             if (m_usageManager.IsUsed(m_symbol))
  67             {
  68                 writer.Write(separator);
  69                 m_builder.WriteSql(writer, sqlGenerator);
  70                 return true;
  71             }
  72             return false;
  73         }
  74         #endregion
  75     }
  76 }