Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

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

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+//---------------------------------------------------------------------
+// <copyright file="OptionalColumn.cs" company="Microsoft">
+//      Copyright (c) Microsoft Corporation.  All rights reserved.
+// </copyright>
+//
+// @owner  [....]
+//---------------------------------------------------------------------
+
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+
+namespace System.Data.SqlClient.SqlGen
+{
+    /// <summary>
+    /// Represents a column in a select list that should be printed only if it is later used.
+    /// Such columns get added by <see cref="SqlGenerator.AddDefaultColumns"/>.
+    /// The SymbolUsageManager associated with the OptionalColumn has the information whether the column
+    /// has been used based on its symbol.
+    /// </summary>
+    internal sealed class OptionalColumn
+    {
+        #region Private State
+        private readonly SymbolUsageManager m_usageManager;
+
+        // The SqlBuilder that contains the column building blocks (e.g: "c.X as X1")
+        private readonly SqlBuilder m_builder = new SqlBuilder();
+
+        // The symbol representing the optional column
+        private readonly Symbol m_symbol;
+        #endregion
+
+        #region Internal Methods
+        /// <summary>
+        /// Append to the "fragment" representing this column
+        /// </summary>
+        internal void Append(object s)
+        {
+            m_builder.Append(s);
+        }
+
+        internal void MarkAsUsed()
+        {
+            this.m_usageManager.MarkAsUsed(this.m_symbol);
+        }
+        #endregion
+
+        #region Constructor
+        internal OptionalColumn(SymbolUsageManager usageManager, Symbol symbol)
+        {
+            this.m_usageManager = usageManager;
+            this.m_symbol = symbol;
+        }
+        #endregion
+
+        #region Internal members
+
+        /// <summary>
+        /// Writes that fragment that represents the optional column 
+        /// if the usage manager says it is used.
+        /// </summary>
+        /// <param name="writer"></param>
+        /// <param name="sqlGenerator"></param>
+        public bool WriteSqlIfUsed(SqlWriter writer, SqlGenerator sqlGenerator, string separator)
+        {
+            if (m_usageManager.IsUsed(m_symbol))
+            {
+                writer.Write(separator);
+                m_builder.WriteSql(writer, sqlGenerator);
+                return true;
+            }
+            return false;
+        }
+        #endregion
+    }
+}