Handle both null and not null checks in queries on not-found='ignore' properties

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

@@ -349,11 +349,23 @@ public async Task NullableEntityProjectionAsync()
 					from x2 in session.Query<NullableOwner>()
 					where x == x2 && x.ManyToOne == null && x.OneToOne.Name == null
 					select x2).ToListAsync());
+
+				var validManyToOne = new OneToOneEntity{Name = "valid"};
+				await (session.SaveAsync(validManyToOne));
+				nullableOwner2.ManyToOne = validManyToOne;
+				await (session.FlushAsync());
+
+				//GH-2988
+				var withNullOrValidList = await (session.Query<NullableOwner>().Where(x => x.ManyToOne.Id == validManyToOne.Id || x.ManyToOne == null).ToListAsync());
+				var withNullOrValidList2 = await (session.Query<NullableOwner>().Where(x =>  x.ManyToOne == null || x.ManyToOne.Id == validManyToOne.Id).ToListAsync());
+
 				Assert.That(fullList.Count, Is.EqualTo(2));
 				Assert.That(withValidManyToOneList.Count, Is.EqualTo(0));
 				Assert.That(withValidManyToOneList2.Count, Is.EqualTo(0));
 				Assert.That(withNullManyToOneList.Count, Is.EqualTo(2));
 				Assert.That(withNullManyToOneJoinedList.Count, Is.EqualTo(2));
+				Assert.That(withNullOrValidList.Count, Is.EqualTo(2));
+				Assert.That(withNullOrValidList2.Count, Is.EqualTo(2));
 			}
 		}
 

src/NHibernate.Test/Hql/EntityJoinHqlTest.cs

@@ -337,11 +337,23 @@ public void NullableEntityProjection()
 					from x2 in session.Query<NullableOwner>()
 					where x == x2 && x.ManyToOne == null && x.OneToOne.Name == null
 					select x2).ToList();
+
+				var validManyToOne = new OneToOneEntity{Name = "valid"};
+				session.Save(validManyToOne);
+				nullableOwner2.ManyToOne = validManyToOne;
+				session.Flush();
+
+				//GH-2988
+				var withNullOrValidList = session.Query<NullableOwner>().Where(x => x.ManyToOne.Id == validManyToOne.Id || x.ManyToOne == null).ToList();
+				var withNullOrValidList2 = session.Query<NullableOwner>().Where(x =>  x.ManyToOne == null || x.ManyToOne.Id == validManyToOne.Id).ToList();
+
 				Assert.That(fullList.Count, Is.EqualTo(2));
 				Assert.That(withValidManyToOneList.Count, Is.EqualTo(0));
 				Assert.That(withValidManyToOneList2.Count, Is.EqualTo(0));
 				Assert.That(withNullManyToOneList.Count, Is.EqualTo(2));
 				Assert.That(withNullManyToOneJoinedList.Count, Is.EqualTo(2));
+				Assert.That(withNullOrValidList.Count, Is.EqualTo(2));
+				Assert.That(withNullOrValidList2.Count, Is.EqualTo(2));
 			}
 		}
 

src/NHibernate/Engine/JoinSequence.cs

@@ -43,7 +43,7 @@ private sealed class Join
 		{
 			private readonly IAssociationType associationType;
 			private readonly IJoinable joinable;
-			private readonly JoinType joinType;
+			private JoinType joinType;
 			private readonly string alias;
 			private readonly string[] lhsColumns;
 
@@ -75,6 +75,7 @@ public IJoinable Joinable
 			public JoinType JoinType
 			{
 				get { return joinType; }
+				internal set { joinType = value; }
 			}
 
 			public string[] LHSColumns
@@ -329,5 +330,11 @@ public interface ISelector
 		public ISessionFactoryImplementor Factory => factory;
 
 		internal bool ForceFilter { get; set; }
+
+		internal void SetJoinType(JoinType joinType)
+		{
+			joins[0].JoinType = joinType;
+			SetUseThetaStyle(false);
+		}
 	}
 }

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

@@ -417,13 +417,8 @@ private void DereferenceEntity(EntityType entityType, bool implicitJoin, string
 
 			if ( joinIsNeeded )
 			{
-				if (comparisonWithNullableEntity && Walker.IsNullComparison)
-				{
-					implicitJoin = false;
-					_joinType = JoinType.LeftOuterJoin;
-				}
-
-				DereferenceEntityJoin( classAlias, entityType, implicitJoin, parent );
+				var forceLeftJoin = comparisonWithNullableEntity && Walker.IsNullComparison;
+				DereferenceEntityJoin(classAlias, entityType, implicitJoin, parent, forceLeftJoin);
 				if (comparisonWithNullableEntity)
 				{
 					_columns = FromElement.GetIdentityColumns();
@@ -457,7 +452,7 @@ private void DereferenceEntityIdentifier(string propertyName, DotNode dotParent)
 			}
 		}
 
-		private void DereferenceEntityJoin(string classAlias, EntityType propertyType, bool impliedJoin, IASTNode parent)
+		private void DereferenceEntityJoin(string classAlias, EntityType propertyType, bool impliedJoin, IASTNode parent, bool forceLeftJoin)
 		{
 			_dereferenceType = DerefEntity;
 			if ( Log.IsDebugEnabled() ) 
@@ -476,7 +471,11 @@ private void DereferenceEntityJoin(string classAlias, EntityType propertyType, b
 			string[] joinColumns = GetColumns();
 			string joinPath = Path;
 
-			if ( impliedJoin && Walker.IsInFrom ) 
+			if (forceLeftJoin)
+			{
+				_joinType = JoinType.LeftOuterJoin;
+			}
+			else if (impliedJoin && Walker.IsInFrom)
 			{
 				_joinType = Walker.ImpliedJoinType;
 			}
@@ -524,7 +523,7 @@ private void DereferenceEntityJoin(string classAlias, EntityType propertyType, b
 				// If this is an implied join in a from element, then use the impled join type which is part of the
 				// tree parser's state (set by the gramamar actions).
 				JoinSequence joinSequence = SessionFactoryHelper
-					.CreateJoinSequence( impliedJoin, propertyType, tableAlias, _joinType, joinColumns );
+					.CreateJoinSequence(!forceLeftJoin && impliedJoin, propertyType, tableAlias, _joinType, joinColumns);
 
 				var factory = new FromElementFactory(
 						currentFromClause,
@@ -545,6 +544,10 @@ private void DereferenceEntityJoin(string classAlias, EntityType propertyType, b
 			}
 			else 
 			{
+				if (forceLeftJoin)
+				{
+					elem.JoinSequence.SetJoinType(_joinType);
+				}
 				currentFromClause.AddDuplicateAlias(classAlias, elem);
 			}