Fix for queries with implicit joins

Author: bahusoid

src/NHibernate.Test/Async/Hql/EntityJoinHqlTest.cs

@@ -11,10 +11,10 @@
 using System.Linq;
 using System.Text.RegularExpressions;
 using NHibernate.Cfg.MappingSchema;
+using NHibernate.Linq;
 using NHibernate.Mapping.ByCode;
 using NHibernate.Test.Hql.EntityJoinHqlTestEntities;
 using NUnit.Framework;
-using NHibernate.Linq;
 
 namespace NHibernate.Test.Hql
 {
@@ -298,26 +298,34 @@ public async Task NullableOneIsNullLinqAsync()
 		{
 			using (var session = OpenSession())
 			{
-				var entity = await (session.Query<NullableOwner>().Where(x => x.OneToOne == null).FirstOrDefaultAsync());
+				var entity = await (session.Query<NullableOwner>().Where(x => x.OneToOne == null).SingleOrDefaultAsync());
+				Assert.That(entity, Is.Not.Null);
+			}
+		}
+
+		[Test(Description = "GH-2611")]
+		public async Task NullableOneFetchIsNullLinqAsync()
+		{
+			using (var session = OpenSession())
+			{
+				var entity = await (session.Query<NullableOwner>().Fetch(x => x.OneToOne).Where(x => x.OneToOne == null).SingleOrDefaultAsync());
 				Assert.That(entity, Is.Not.Null);
 			}
 		}
 
 		[Test]
 		public async Task NullableOneToOneFetchQueryIsNotAffected2Async()
 		{
-			using (var sqlLog = new SqlLogSpy())
 			using (var session = OpenSession())
 			{
-				var entities =
+				var entity =
 					await (session
 						.CreateQuery(
 							"select ex "
 							+ "from NullableOwner ex left join fetch ex.OneToOne o "
 							+ "where o.Id is null "
 						)
-						.ListAsync<NullableOwner>());
-				var entity = entities[0];
+						.UniqueResultAsync<NullableOwner>());
 
 				Assert.That(entity, Is.Not.Null);
 				Assert.That(Regex.Matches(sqlLog.GetWholeLog(), "OneToOneEntity").Count, Is.EqualTo(1));

src/NHibernate.Test/Hql/EntityJoinHqlTest.cs

@@ -1,6 +1,7 @@
 using System.Linq;
 using System.Text.RegularExpressions;
 using NHibernate.Cfg.MappingSchema;
+using NHibernate.Linq;
 using NHibernate.Mapping.ByCode;
 using NHibernate.Test.Hql.EntityJoinHqlTestEntities;
 using NUnit.Framework;
@@ -286,26 +287,34 @@ public void NullableOneIsNullLinq()
 		{
 			using (var session = OpenSession())
 			{
-				var entity = session.Query<NullableOwner>().Where(x => x.OneToOne == null).FirstOrDefault();
+				var entity = session.Query<NullableOwner>().Where(x => x.OneToOne == null).SingleOrDefault();
+				Assert.That(entity, Is.Not.Null);
+			}
+		}
+
+		[Test(Description = "GH-2611")]
+		public void NullableOneFetchIsNullLinq()
+		{
+			using (var session = OpenSession())
+			{
+				var entity = session.Query<NullableOwner>().Fetch(x => x.OneToOne).Where(x => x.OneToOne == null).SingleOrDefault();
 				Assert.That(entity, Is.Not.Null);
 			}
 		}
 
 		[Test]
 		public void NullableOneToOneFetchQueryIsNotAffected2()
 		{
-			using (var sqlLog = new SqlLogSpy())
 			using (var session = OpenSession())
 			{
-				var entities =
+				var entity =
 					session
 						.CreateQuery(
 							"select ex "
 							+ "from NullableOwner ex left join fetch ex.OneToOne o "
 							+ "where o.Id is null "
 						)
-						.List<NullableOwner>();
-				var entity = entities[0];
+						.UniqueResult<NullableOwner>();
 
 				Assert.That(entity, Is.Not.Null);
 				Assert.That(Regex.Matches(sqlLog.GetWholeLog(), "OneToOneEntity").Count, Is.EqualTo(1));

src/NHibernate/Hql/Ast/ANTLR/Tree/DotNode.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Linq;
 using Antlr.Runtime;
 
 using NHibernate.Engine;
@@ -412,7 +413,11 @@ private void DereferenceEntity(EntityType entityType, bool implicitJoin, string
 				if (Walker.IsComparativeExpressionClause && entityType.IsNullable)
 				{
 					joinIsNeeded = comparisonWithNullableEntity = true;
-					_joinType = JoinType.LeftOuterJoin;
+
+					//TODO: Fix this hack. We should always left join here. Skip left join for nullable entity if query contains implicit joins. We currently don't support such queries (see OneToOneCompositeQueryCompareWithJoin)
+					var fromJoins = ASTUtil.CollectChildren<FromElement>(Walker.CurrentFromClause, x => x is FromElement fe && !fe.IsImplied && fe.Type == HqlSqlWalker.FROM_FRAGMENT);
+					if(fromJoins.Count == 1)
+						_joinType = JoinType.LeftOuterJoin;
 				}
 				else
 				{