Fix Linq Fetch over component after fetching an association (#2517)

Fixes #2511

Co-authored-by: Roman Artiukhin <bahusdrive@gmail.com>

Author: maca88

src/NHibernate.Test/Async/FetchLazyProperties/FetchLazyPropertiesFixture.cs

@@ -666,6 +666,40 @@ private static void AssertFetchComponentManyToOne(Person person)
 
 		#endregion
 
+		#region TestHqlFetchManyToOneAndComponentManyToOne
+
+		[Test]
+		public async Task TestHqlFetchManyToOneAndComponentManyToOneAsync()
+		{
+			Person person;
+			using (var s = OpenSession())
+			{
+				person = await (s.CreateQuery("from Person p fetch p.Address left join fetch p.Address.Continent left join fetch p.BestFriend where p.Id = 1").UniqueResultAsync<Person>());
+			}
+
+			AssertFetchManyToOneAndComponentManyToOne(person);
+		}
+
+		[Test]
+		public async Task TestLinqFetchManyToOneAndComponentManyToOneAsync()
+		{
+			Person person;
+			using (var s = OpenSession())
+			{
+				person = await (s.Query<Person>().Fetch(o => o.BestFriend).Fetch(o => o.Address).ThenFetch(o => o.Continent).FirstOrDefaultAsync(o => o.Id == 1));
+			}
+
+			AssertFetchManyToOneAndComponentManyToOne(person);
+		}
+
+		private static void AssertFetchManyToOneAndComponentManyToOne(Person person)
+		{
+			AssertFetchComponentManyToOne(person);
+			Assert.That(NHibernateUtil.IsInitialized(person.BestFriend), Is.True);
+		}
+
+		#endregion
+
 		#region FetchSubClassFormula
 
 		[Test]

src/NHibernate.Test/FetchLazyProperties/FetchLazyPropertiesFixture.cs

@@ -655,6 +655,40 @@ private static void AssertFetchComponentManyToOne(Person person)
 
 		#endregion
 
+		#region TestHqlFetchManyToOneAndComponentManyToOne
+
+		[Test]
+		public void TestHqlFetchManyToOneAndComponentManyToOne()
+		{
+			Person person;
+			using (var s = OpenSession())
+			{
+				person = s.CreateQuery("from Person p fetch p.Address left join fetch p.Address.Continent left join fetch p.BestFriend where p.Id = 1").UniqueResult<Person>();
+			}
+
+			AssertFetchManyToOneAndComponentManyToOne(person);
+		}
+
+		[Test]
+		public void TestLinqFetchManyToOneAndComponentManyToOne()
+		{
+			Person person;
+			using (var s = OpenSession())
+			{
+				person = s.Query<Person>().Fetch(o => o.BestFriend).Fetch(o => o.Address).ThenFetch(o => o.Continent).FirstOrDefault(o => o.Id == 1);
+			}
+
+			AssertFetchManyToOneAndComponentManyToOne(person);
+		}
+
+		private static void AssertFetchManyToOneAndComponentManyToOne(Person person)
+		{
+			AssertFetchComponentManyToOne(person);
+			Assert.That(NHibernateUtil.IsInitialized(person.BestFriend), Is.True);
+		}
+
+		#endregion
+
 		#region FetchSubClassFormula
 
 		[Test]

src/NHibernate/Linq/IntermediateHqlTree.cs

@@ -127,6 +127,11 @@ public void AddFromClause(HqlTreeNode from)
 			_root.NodesPreOrder.OfType<HqlFrom>().First().AddChild(from);
 		}
 
+		internal HqlRange GetFromRangeClause()
+		{
+			return _root.NodesPreOrder.OfType<HqlFrom>().First().Children.OfType<HqlRange>().FirstOrDefault();
+		}
+
 		public void AddSelectClause(HqlTreeNode select)
 		{
 			_root.NodesPreOrder.OfType<HqlSelectFrom>().First().AddChild(select);

src/NHibernate/Linq/Visitors/ResultOperatorProcessors/ProcessFetch.cs

@@ -19,15 +19,31 @@ public void Process(FetchRequestBase resultOperator, QueryModelVisitor queryMode
 		}
 
 		public void Process(FetchRequestBase resultOperator, QueryModelVisitor queryModelVisitor, IntermediateHqlTree tree, string sourceAlias)
+		{
+			Process(resultOperator, queryModelVisitor, tree, null, sourceAlias);
+		}
+
+		private void Process(
+			FetchRequestBase resultOperator,
+			QueryModelVisitor queryModelVisitor,
+			IntermediateHqlTree tree,
+			HqlTreeNode currentNode,
+			string sourceAlias)
 		{
 			var memberPath = tree.TreeBuilder.Dot(
 				tree.TreeBuilder.Ident(sourceAlias),
 				tree.TreeBuilder.Ident(resultOperator.RelationMember.Name));
 
-			Process(resultOperator, queryModelVisitor, tree, memberPath, null);
+			Process(resultOperator, queryModelVisitor, tree, memberPath, currentNode, null);
 		}
 
-		private void Process(FetchRequestBase resultOperator, QueryModelVisitor queryModelVisitor, IntermediateHqlTree tree, HqlDot memberPath, IType propType)
+		private void Process(
+			FetchRequestBase resultOperator,
+			QueryModelVisitor queryModelVisitor,
+			IntermediateHqlTree tree,
+			HqlDot memberPath,
+			HqlTreeNode currentNode,
+			IType propType)
 		{
 			if (resultOperator is FetchOneRequest)
 			{
@@ -40,8 +56,14 @@ private void Process(FetchRequestBase resultOperator, QueryModelVisitor queryMod
 
 				if (propType != null && !propType.IsAssociationType)
 				{
-					tree.AddFromLastChildClause(tree.TreeBuilder.Fetch());
-					tree.AddFromLastChildClause(memberPath);
+					if (currentNode == null)
+					{
+						currentNode = tree.GetFromRangeClause()
+									?? throw new InvalidOperationException($"Property {resultOperator.RelationMember.Name} cannot be fetched for this type of query.");
+					}
+
+					currentNode.AddChild(tree.TreeBuilder.Fetch());
+					currentNode.AddChild(memberPath);
 
 					ComponentType componentType = null;
 					foreach (var innerFetch in resultOperator.InnerFetchRequests)
@@ -61,20 +83,21 @@ private void Process(FetchRequestBase resultOperator, QueryModelVisitor queryMod
 							memberPath,
 							tree.TreeBuilder.Ident(innerFetch.RelationMember.Name));
 
-						Process(innerFetch, queryModelVisitor, tree, memberPath, componentType.Subtypes[subTypeIndex]);
+						Process(innerFetch, queryModelVisitor, tree, memberPath, currentNode, componentType.Subtypes[subTypeIndex]);
 					}
 
 					return;
 				}
 			}
 
 			var alias = queryModelVisitor.Model.GetNewName("_");
-			tree.AddFromClause(tree.TreeBuilder.LeftFetchJoin(memberPath, tree.TreeBuilder.Alias(alias)));
+			currentNode = tree.TreeBuilder.LeftFetchJoin(memberPath, tree.TreeBuilder.Alias(alias));
+			tree.AddFromClause(currentNode);
 			tree.AddDistinctRootOperator();
 
 			foreach (var innerFetch in resultOperator.InnerFetchRequests)
 			{
-				Process(innerFetch, queryModelVisitor, tree, alias);
+				Process(innerFetch, queryModelVisitor, tree, currentNode, alias);
 			}
 		}
 	}