Fix inner join issue when referenced in Where clause in LINQ (nhibernate#3110)

Author: bahusoid

src/NHibernate.Test/Async/Linq/ByMethod/JoinTests.cs

@@ -111,6 +111,23 @@ public async Task LeftJoinExtensionMethodWithMultipleKeyPropertiesAsync()
 			}
 		}
 
+		[Test(Description = "GH-3104")]
+		public async Task LeftJoinExtensionMethodWithInnerJoinAfterAsync()
+		{
+			var animals = await (db.Animals
+						   .LeftJoin(db.Mammals, o => o.Id, i => i.Id, (o, i) => new { animal = o, mammalLeft1 = i })
+						   .LeftJoin(db.Mammals, x => x.mammalLeft1.Id, y => y.Id, (o, i) => new { o.animal, o.mammalLeft1, mammalLeft2 = i })
+						   .Join(db.Mammals, o => o.mammalLeft2.Id, y => y.Id, (o, i) => new { o.animal, o.mammalLeft1, o.mammalLeft2, mammalInner = i })
+						   .Where(x => x.mammalLeft1.SerialNumber.StartsWith("9"))
+						   .Where(x => x.mammalLeft2.SerialNumber.StartsWith("9"))
+						   .Where(x => x.animal.SerialNumber.StartsWith("9"))
+						   .Where(x => x.mammalInner.SerialNumber.StartsWith("9"))
+						   .Select(x => new { SerialNumber = x.animal.SerialNumber })
+						   .ToListAsync());
+
+			Assert.That(animals.Count, Is.EqualTo(1));
+		}
+
 		[Test]
 		public async Task LeftJoinExtensionMethodWithOuterReferenceInWhereClauseOnlyAsync()
 		{

src/NHibernate.Test/Linq/ByMethod/JoinTests.cs

@@ -99,6 +99,23 @@ public void LeftJoinExtensionMethodWithMultipleKeyProperties()
 			}
 		}
 
+		[Test(Description = "GH-3104")]
+		public void LeftJoinExtensionMethodWithInnerJoinAfter()
+		{
+			var animals = db.Animals
+						   .LeftJoin(db.Mammals, o => o.Id, i => i.Id, (o, i) => new { animal = o, mammalLeft1 = i })
+						   .LeftJoin(db.Mammals, x => x.mammalLeft1.Id, y => y.Id, (o, i) => new { o.animal, o.mammalLeft1, mammalLeft2 = i })
+						   .Join(db.Mammals, o => o.mammalLeft2.Id, y => y.Id, (o, i) => new { o.animal, o.mammalLeft1, o.mammalLeft2, mammalInner = i })
+						   .Where(x => x.mammalLeft1.SerialNumber.StartsWith("9"))
+						   .Where(x => x.mammalLeft2.SerialNumber.StartsWith("9"))
+						   .Where(x => x.animal.SerialNumber.StartsWith("9"))
+						   .Where(x => x.mammalInner.SerialNumber.StartsWith("9"))
+						   .Select(x => new { SerialNumber = x.animal.SerialNumber })
+						   .ToList();
+
+			Assert.That(animals.Count, Is.EqualTo(1));
+		}
+
 		[Test]
 		public void LeftJoinExtensionMethodWithOuterReferenceInWhereClauseOnly()
 		{

src/NHibernate/Linq/GroupJoin/GroupJoinAggregateDetectionVisitor.cs

@@ -1,10 +1,8 @@
 using System;
 using System.Collections.Generic;
-using System.Collections.ObjectModel;
 using System.Linq.Expressions;
 using NHibernate.Linq.Expressions;
 using NHibernate.Linq.Visitors;
-using Remotion.Linq;
 using Remotion.Linq.Clauses;
 using Remotion.Linq.Clauses.Expressions;
 
@@ -63,13 +61,13 @@ protected override Expression VisitMember(MemberExpression expression)
 
 		protected override Expression VisitQuerySourceReference(QuerySourceReferenceExpression expression)
 		{
-			var fromClause = (FromClauseBase) expression.ReferencedQuerySource;
-
-			var querySourceReference = fromClause.FromExpression as QuerySourceReferenceExpression;
-			if (querySourceReference != null)
+			if (!(expression.ReferencedQuerySource is FromClauseBase fromClause))
+			{
+			}
+			else if (fromClause.FromExpression is QuerySourceReferenceExpression querySourceReference)
 			{
-				var groupJoinClause = querySourceReference.ReferencedQuerySource as GroupJoinClause;
-				if (groupJoinClause != null && _groupJoinClauses.Contains(groupJoinClause))
+				if (querySourceReference.ReferencedQuerySource is GroupJoinClause groupJoinClause &&
+				    _groupJoinClauses.Contains(groupJoinClause))
 				{
 					if (_inAggregate.FlagIsFalse)
 					{