Fix enum detection when using OfType for Linq provider

Author: maca88

src/NHibernate.DomainModel/Northwind/Entities/Animal.cs

@@ -19,6 +19,8 @@ public class Animal
     public abstract class Reptile : Animal
     {
         public virtual double BodyTemperature { get; set; }
+
+		public virtual EnumStoredAsString Enum1 { get; set; }
     }
 
     public class Lizard : Reptile { }

src/NHibernate.DomainModel/Northwind/Mappings/Animal.hbm.xml

@@ -19,6 +19,9 @@
     <joined-subclass name="Reptile">
       <key column="Animal"/>
       <property name="BodyTemperature"/>
+      <property name="Enum1" type="NHibernate.DomainModel.Northwind.Entities.EnumStoredAsStringType, NHibernate.DomainModel"
+                formula="('Unspecified')" insert="false" update="false">
+      </property>
 
       <joined-subclass name="Lizard">
         <key column="Reptile"/>
@@ -39,4 +42,4 @@
       </joined-subclass>
     </joined-subclass>
   </class>
-</hibernate-mapping>
+</hibernate-mapping>

src/NHibernate.Test/Linq/ParameterTypeLocatorTests.cs

@@ -84,6 +84,19 @@ public void EqualStringEnumTest()
 			);
 		}
 
+		[Test]
+		public void SubClassStringEnumTest()
+		{
+			AssertResults(
+				new Dictionary<string, Predicate<IType>>
+				{
+					{"0", o => o is EnumStoredAsStringType}
+				},
+				db.Animals.Where(o => o.Children.OfType<Reptile>().Any(r => r.Enum1 == EnumStoredAsString.Unspecified)),
+				db.Animals.Where(o => o.Children.OfType<Reptile>().Any(r => EnumStoredAsString.Unspecified == r.Enum1))
+			);
+		}
+
 		[Test]
 		public void EqualsMethodStringTest()
 		{

src/NHibernate/Util/ExpressionsHelper.cs

@@ -16,6 +16,7 @@
 using NHibernate.Type;
 using Remotion.Linq.Clauses;
 using Remotion.Linq.Clauses.Expressions;
+using Remotion.Linq.Clauses.ResultOperators;
 using Remotion.Linq.Parsing;
 
 namespace NHibernate.Util
@@ -716,6 +717,12 @@ protected override Expression VisitQuerySourceReference(QuerySourceReferenceExpr
 
 			protected override Expression VisitSubQuery(SubQueryExpression expression)
 			{
+				var ofTypeOperator = expression.QueryModel.ResultOperators.OfType<OfTypeResultOperator>().FirstOrDefault();
+				if (ofTypeOperator != null)
+				{
+					_convertType = ofTypeOperator.SearchedItemType;
+				}
+
 				base.Visit(expression.QueryModel.SelectClause.Selector);
 				return expression;
 			}