NH-3190 - Port-back fix

HqlGeneratorExpressionTreeVisitor should not convert boolean equality operator to case operator when node is a sub-query with single or first result operators

Author: hazzik

src/NHibernate.Test/Linq/WhereSubqueryTests.cs

@@ -547,5 +547,61 @@ public void SubqueryWhereFailingTest3()
 
 			Assert.That(list.Count, Is.EqualTo(2155));
 		}
+
+		[Test]
+		public void ProductsWithSubqueryReturningBoolFirstOrDefaultEq()
+		{
+			//NH-3190
+			var result = (from p in db.Products
+						  where (from c in db.Categories
+								 where c.Name == "Confections"
+								 && c == p.Category
+								 select p.Discontinued).FirstOrDefault() == false
+						  select p)
+				.ToList();
+
+			Assert.That(result.Count, Is.EqualTo(13));
+		}
+
+		[Test]
+		public void CategoriesWithFirstProductIsNotDiscouned()
+		{
+			//NH-3190
+			var result = (from c in db.Categories
+						  where c.Products.Select(p => p.Discontinued).FirstOrDefault() == false
+						  select c).ToList();
+
+			Assert.That(result.Count, Is.EqualTo(7));
+		}
+
+		[Test, Ignore("Not fixed yet.")]
+		public void ProductsWithSubqueryReturningProjectionBoolFirstOrDefaultEq()
+		{
+			//NH-3190
+			var result = (from p in db.Products
+						  where (from c in db.Categories
+								 where c.Name == "Confections"
+								 && c == p.Category
+								 select new{R=p.Discontinued}).FirstOrDefault().R == false
+						  select p)
+				.ToList();
+
+			Assert.That(result.Count, Is.EqualTo(13));
+		}
+
+		[Test]
+		public void ProductsWithSubqueryReturningStringFirstOrDefaultEq()
+		{
+			//NH-3190
+			var result = (from p in db.Products
+						  where (from c in db.Categories
+								 where c.Name == "Confections"
+								 && c == p.Category
+								 select p.Name).FirstOrDefault() == p.Name
+						  select p)
+				.ToList();
+
+			Assert.That(result.Count, Is.EqualTo(13));
+		}
 	}
 }

src/NHibernate/Linq/Visitors/HqlGeneratorExpressionTreeVisitor.cs

@@ -7,6 +7,7 @@
 using NHibernate.Linq.Functions;
 using NHibernate.Param;
 using Remotion.Linq.Clauses.Expressions;
+using Remotion.Linq.Clauses.ResultOperators;
 
 namespace NHibernate.Linq.Visitors
 {
@@ -327,6 +328,18 @@ private HqlExpression GetExpressionForBooleanEquality(Expression @operator, HqlE
 				return original;
 			}
 
+			var subQueryExpression = @operator as SubQueryExpression;
+			if (subQueryExpression != null)
+			{
+				var resultOperators = subQueryExpression.QueryModel.ResultOperators;
+				if (resultOperators.Count == 1 &&
+					(resultOperators[0] is FirstResultOperator ||
+					 resultOperators[0] is SingleResultOperator))
+				{
+					return original;
+				}
+			}
+
 			//When the expression is a member-access nullable then use the "case" clause to transform it to boolean (to use always .NET meaning instead leave the DB the behavior for null)
 			//When the expression is a complex-expression then use the "case" clause to transform it to boolean
 			return _hqlTreeBuilder.Case(new[] {_hqlTreeBuilder.When(original, _hqlTreeBuilder.True())}, _hqlTreeBuilder.False());