--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Source/Data/Linq/Builder/CountBuilder.cs	Thu Mar 27 21:46:09 2014 +0400
@@ -0,0 +1,162 @@
+using System;
+using System.Linq.Expressions;
+
+namespace BLToolkit.Data.Linq.Builder
+{
+	using BLToolkit.Linq;
+	using Data.Sql;
+
+	class CountBuilder : MethodCallBuilder
+	{
+		public static string[] MethodNames = new[] { "Count", "LongCount" };
+
+		protected override bool CanBuildMethodCall(ExpressionBuilder builder, MethodCallExpression methodCall, BuildInfo buildInfo)
+		{
+			return methodCall.IsQueryable(MethodNames);
+		}
+
+		protected override IBuildContext BuildMethodCall(ExpressionBuilder builder, MethodCallExpression methodCall, BuildInfo buildInfo)
+		{
+			var returnType = methodCall.Method.ReturnType;
+			var sequence   = builder.BuildSequence(new BuildInfo(buildInfo, methodCall.Arguments[0]));
+
+			if (sequence.SqlQuery != buildInfo.SqlQuery)
+			{
+				if (sequence is JoinBuilder.GroupJoinSubQueryContext)
+				{
+					var ctx = new CountContext(buildInfo.Parent, sequence, returnType)
+					{
+						SqlQuery = ((JoinBuilder.GroupJoinSubQueryContext)sequence).GetCounter(methodCall)
+					};
+
+					ctx.Sql        = ctx.SqlQuery;
+					ctx.FieldIndex = ctx.SqlQuery.Select.Add(SqlFunction.CreateCount(returnType, ctx.SqlQuery), "cnt");
+
+					return ctx;
+				}
+
+				if (sequence is GroupByBuilder.GroupByContext)
+				{
+					return new CountContext(buildInfo.Parent, sequence, returnType)
+					{
+						Sql        = SqlFunction.CreateCount(returnType, sequence.SqlQuery),
+						FieldIndex = -1
+					};
+				}
+			}
+
+			if (sequence.SqlQuery.Select.IsDistinct        ||
+			    sequence.SqlQuery.Select.TakeValue != null ||
+			    sequence.SqlQuery.Select.SkipValue != null ||
+			   !sequence.SqlQuery.GroupBy.IsEmpty)
+			{
+				sequence.ConvertToIndex(null, 0, ConvertFlags.Key);
+				sequence = new SubQueryContext(sequence);
+			}
+
+			if (sequence.SqlQuery.OrderBy.Items.Count > 0)
+			{
+				if (sequence.SqlQuery.Select.TakeValue == null && sequence.SqlQuery.Select.SkipValue == null)
+					sequence.SqlQuery.OrderBy.Items.Clear();
+				else
+					sequence = new SubQueryContext(sequence);
+			}
+
+			var context = new CountContext(buildInfo.Parent, sequence, returnType);
+
+			context.Sql        = context.SqlQuery;
+			context.FieldIndex = context.SqlQuery.Select.Add(SqlFunction.CreateCount(returnType, context.SqlQuery), "cnt");
+
+			return context;
+		}
+
+		protected override SequenceConvertInfo Convert(
+			ExpressionBuilder builder, MethodCallExpression methodCall, BuildInfo buildInfo, ParameterExpression param)
+		{
+			return null;
+		}
+
+		internal class CountContext : SequenceContextBase
+		{
+			public CountContext(IBuildContext parent, IBuildContext sequence, Type returnType)
+				: base(parent, sequence, null)
+			{
+				_returnType = returnType;
+			}
+
+			readonly Type      _returnType;
+			private  SqlInfo[] _index;
+
+			public int            FieldIndex;
+			public ISqlExpression Sql;
+
+			public override void BuildQuery<T>(Query<T> query, ParameterExpression queryParameter)
+			{
+				var expr   = Builder.BuildSql(_returnType, FieldIndex);
+				var mapper = Builder.BuildMapper<object>(expr);
+
+				query.SetElementQuery(mapper.Compile());
+			}
+
+			public override Expression BuildExpression(Expression expression, int level)
+			{
+				return Builder.BuildSql(_returnType, ConvertToIndex(expression, level, ConvertFlags.Field)[0].Index);
+			}
+
+			public override SqlInfo[] ConvertToSql(Expression expression, int level, ConvertFlags flags)
+			{
+				switch (flags)
+				{
+					case ConvertFlags.Field : return new[] { new SqlInfo { Query = Parent.SqlQuery, Sql = Sql } };
+				}
+
+				throw new InvalidOperationException();
+			}
+
+			public override SqlInfo[] ConvertToIndex(Expression expression, int level, ConvertFlags flags)
+			{
+				switch (flags)
+				{
+					case ConvertFlags.Field :
+						return _index ?? (_index = new[]
+						{
+							new SqlInfo { Query = Parent.SqlQuery, Index = Parent.SqlQuery.Select.Add(Sql), Sql = Sql, }
+						});
+				}
+
+				throw new InvalidOperationException();
+			}
+
+			public override IsExpressionResult IsExpression(Expression expression, int level, RequestFor requestFlag)
+			{
+				switch (requestFlag)
+				{
+					case RequestFor.Expression : return IsExpressionResult.True;
+				}
+
+				return IsExpressionResult.False;
+			}
+
+			public override IBuildContext GetContext(Expression expression, int level, BuildInfo buildInfo)
+			{
+				return Sequence.GetContext(expression, level, buildInfo);
+			}
+
+			public override ISqlExpression GetSubQuery(IBuildContext context)
+			{
+				var query = context.SqlQuery;
+
+				if (query == SqlQuery)
+				{
+					var col = query.Select.Columns[query.Select.Columns.Count - 1];
+
+					query.Select.Columns.RemoveAt(query.Select.Columns.Count - 1);
+
+					return col.Expression;
+				}
+
+				return null;
+			}
+		}
+	}
+}