Unit and partial fix for NH2504

Author: Gunnar Liljas

src/NHibernate.Test/Linq/QueryCacheableTests.cs

@@ -114,5 +114,36 @@ public void CacheableRegionBeforeOtherClauses()
             Assert.That(Sfi.Statistics.QueryCachePutCount, Is.EqualTo(2));
             Assert.That(Sfi.Statistics.QueryCacheHitCount, Is.EqualTo(1));
         }
+
+		  [Test]
+		  public void GroupByQueryIsCacheable()
+		  {
+			  Sfi.Statistics.Clear();
+			  Sfi.QueryCache.Clear();
+
+			  var c = db
+				  .Customers
+				  .GroupBy(x => x.Address.Country)
+				  .Select(x => x.Key)
+				  .Cacheable()
+				  .ToList();
+
+			  c = db
+				 .Customers
+				 .GroupBy(x => x.Address.Country)
+				 .Select(x => x.Key)
+				 .ToList();
+
+			  c = db
+				 .Customers
+				 .GroupBy(x => x.Address.Country)
+				 .Select(x => x.Key)
+				 .Cacheable()
+				 .ToList();
+
+			  Assert.That(Sfi.Statistics.QueryExecutionCount, Is.EqualTo(2));
+			  Assert.That(Sfi.Statistics.QueryCachePutCount, Is.EqualTo(1));
+			  Assert.That(Sfi.Statistics.QueryCacheHitCount, Is.EqualTo(1));
+		  }
     }
 }

src/NHibernate/Linq/GroupBy/AggregatingGroupByRewriter.cs

@@ -38,6 +38,7 @@ public static class AggregatingGroupByRewriter
 				typeof (AnyResultOperator),
 				typeof (AllResultOperator),
 				typeof (TimeoutResultOperator),
+				typeof (CacheableResultOperator)
 			};
 
 		public static void ReWrite(QueryModel queryModel)