NH-3787 - Fix decimal truncation in some Linq queries

Author: fredericDelaporte

src/NHibernate.Test/NHSpecificTest/NH3787/TestFixture.cs

@@ -70,7 +70,7 @@ public void TestLinqProjection()
 			}
 		}
 
-		[Test, Ignore("Not fixed yet.")]
+		[Test]
 		public void TestLinqQueryOnExpression()
 		{
 			using (var s = OpenSession())

src/NHibernate/Dialect/Dialect.cs

@@ -98,6 +98,7 @@ protected Dialect()
 			RegisterFunction("upper", new StandardSQLFunction("upper"));
 			RegisterFunction("lower", new StandardSQLFunction("lower"));
 			RegisterFunction("cast", new CastFunction());
+			RegisterFunction("transparentcast", new TransparentCastFunction());
 			RegisterFunction("extract", new AnsiExtractFunction());
 			RegisterFunction("concat", new VarArgsSQLFunction(NHibernateUtil.String, "(", "||", ")"));
 

src/NHibernate/Dialect/Function/TransparentCastFunction.cs

@@ -0,0 +1,16 @@
+using System;
+
+namespace NHibernate.Dialect.Function
+{
+	/// <summary>
+	/// A HQL only cast for helping HQL knowing the type. Does not generates any actual cast in code.
+	/// </summary>
+	[Serializable]
+	public class TransparentCastFunction : CastFunction
+	{
+		protected override bool CastingIsRequired(string sqlType)
+		{
+			return false;
+		}
+	}
+}

src/NHibernate/Hql/Ast/ANTLR/SessionFactoryHelperExtensions.cs

@@ -77,7 +77,7 @@ public IType FindFunctionReturnType(String functionName, IASTNode first)
 
 			if (first != null)
 			{
-				if (functionName == "cast")
+				if (sqlFunction is CastFunction)
 				{
 					argumentType = TypeFactory.HeuristicType(first.NextSibling.Text);
 				}

src/NHibernate/Hql/Ast/HqlTreeBuilder.cs

@@ -301,6 +301,11 @@ public HqlCast Cast(HqlExpression expression, System.Type type)
 			return new HqlCast(_factory, expression, type);
 		}
 
+		public HqlTransparentCast TransparentCast(HqlExpression expression, System.Type type)
+		{
+			return new HqlTransparentCast(_factory, expression, type);
+		}
+
 		public HqlBitwiseNot BitwiseNot()
 		{
 			return new HqlBitwiseNot(_factory);

src/NHibernate/Hql/Ast/HqlTreeNode.cs

@@ -701,6 +701,16 @@ public HqlCast(IASTFactory factory, HqlExpression expression, System.Type type)
 		}
 	}
 
+	public class HqlTransparentCast : HqlExpression
+	{
+		public HqlTransparentCast(IASTFactory factory, HqlExpression expression, System.Type type)
+			: base(HqlSqlWalker.METHOD_CALL, "method", factory)
+		{
+			AddChild(new HqlIdent(factory, "transparentcast"));
+			AddChild(new HqlExpressionList(factory, expression, new HqlIdent(factory, type)));
+		}
+	}
+
 	public class HqlCoalesce : HqlExpression
 	{
 		public HqlCoalesce(IASTFactory factory, HqlExpression lhs, HqlExpression rhs)

src/NHibernate/Linq/Visitors/HqlGeneratorExpressionVisitor.cs

@@ -540,7 +540,7 @@ protected HqlTreeNode VisitConditionalExpression(ConditionalExpression expressio
 
 			return (expression.Type == typeof (bool) || expression.Type == (typeof (bool?)))
 					   ? @case
-					   : _hqlTreeBuilder.Cast(@case, expression.Type);
+					   : _hqlTreeBuilder.TransparentCast(@case, expression.Type);
 		}
 
 		protected HqlTreeNode VisitSubQueryExpression(SubQueryExpression expression)