Fix joining with an inherited property from another table for Linq provider

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

@@ -148,5 +148,13 @@ public async Task CanJoinOnEntityWithSubclassesAsync()
 						from o2 in db.Animals.Where(x => x.BodyWeight > 50)
 						select new {o, o2}).Take(1).ToListAsync());
 		}
+
+		[Test(Description = "GH-2580")]
+		public async Task CanInnerJoinOnSubclassWithBaseTableReferenceInOnClauseAsync()
+		{
+			var result = await ((from o in db.Animals
+			              join o2 in db.Mammals on o.BodyWeight equals o2.BodyWeight
+			              select new { o, o2 }).Take(1).ToListAsync());
+		}
 	}
 }

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

@@ -137,5 +137,13 @@ public void CanJoinOnEntityWithSubclasses()
 						from o2 in db.Animals.Where(x => x.BodyWeight > 50)
 						select new {o, o2}).Take(1).ToList();
 		}
+
+		[Test(Description = "GH-2580")]
+		public void CanInnerJoinOnSubclassWithBaseTableReferenceInOnClause()
+		{
+			var result = (from o in db.Animals
+			              join o2 in db.Mammals on o.BodyWeight equals o2.BodyWeight
+			              select new { o, o2 }).Take(1).ToList();
+		}
 	}
 }

src/NHibernate/Linq/Visitors/QueryModelVisitor.cs

@@ -3,6 +3,7 @@
 using System.Linq;
 using System.Linq.Expressions;
 using System.Reflection;
+using NHibernate.Engine;
 using NHibernate.Hql.Ast;
 using NHibernate.Linq.Clauses;
 using NHibernate.Linq.Expressions;
@@ -12,6 +13,7 @@
 using NHibernate.Linq.ResultOperators;
 using NHibernate.Linq.ReWriters;
 using NHibernate.Linq.Visitors.ResultOperatorProcessors;
+using NHibernate.Persister.Entity;
 using NHibernate.Util;
 using Remotion.Linq;
 using Remotion.Linq.Clauses;
@@ -527,10 +529,13 @@ private void AddJoin(JoinClause joinClause, QueryModel queryModel, bool innerJoi
 			var withClause = equalityVisitor.Visit(joinClause.InnerKeySelector, joinClause.OuterKeySelector);
 			var alias = _hqlTree.TreeBuilder.Alias(VisitorParameters.QuerySourceNamer.GetName(joinClause));
 			var joinExpression = HqlGeneratorExpressionVisitor.Visit(joinClause.InnerSequence, VisitorParameters);
+			var baseMemberCheker = new BaseMemberChecker(VisitorParameters.SessionFactory);
+
 			HqlTreeNode join;
-			// When associations are located inside the inner key selector we have to use a cross join instead of an inner
-			// join and add the condition in the where statement.
-			if (queryModel.BodyClauses.OfType<NhJoinClause>().Any(o => o.ParentJoinClause == joinClause))
+			// When associations or members from another table are located inside the inner key selector we have to use a cross join
+			// instead of an inner join and add the condition in the where statement.
+			if (queryModel.BodyClauses.OfType<NhJoinClause>().Any(o => o.ParentJoinClause == joinClause) ||
+			    queryModel.BodyClauses.OfType<JoinClause>().Any(baseMemberCheker.ContainsBaseMember))
 			{
 				if (!innerJoin)
 				{
@@ -551,6 +556,54 @@ private void AddJoin(JoinClause joinClause, QueryModel queryModel, bool innerJoi
 			_hqlTree.AddFromClause(join);
 		}
 
+		private class BaseMemberChecker : NhExpressionVisitor
+		{
+			private readonly ISessionFactoryImplementor _sessionFactory;
+			private bool _result;
+
+			public BaseMemberChecker(ISessionFactoryImplementor sessionFactory)
+			{
+				_sessionFactory = sessionFactory;
+			}
+
+			public bool ContainsBaseMember(JoinClause joinClause)
+			{
+				// Visit the join inner key only for entities that have subclasses
+				if (joinClause.InnerSequence is ConstantExpression constantNode &&
+				    constantNode.Value is IEntityNameProvider entityNameProvider &&
+				    !_sessionFactory.GetEntityPersister(entityNameProvider.EntityName).EntityMetamodel.HasSubclasses)
+				{
+					return false;
+				}
+
+				_result = false;
+				Visit(joinClause.InnerKeySelector);
+
+				return _result;
+			}
+
+			protected override Expression VisitMember(MemberExpression node)
+			{
+				if (ExpressionsHelper.TryGetMappedType(
+						_sessionFactory,
+						node,
+						out _,
+						out var persister,
+						out _,
+						out var propertyPath) &&
+					persister is IOuterJoinLoadable joinLoadable &&
+					joinLoadable.EntityMetamodel.GetIdentifierPropertyType(propertyPath) == null &&
+					joinLoadable.GetPropertyTableName(propertyPath) != joinLoadable.TableName
+				)
+				{
+					_result = true;
+					return node;
+				}
+
+				return base.VisitMember(node);
+			}
+		}
+
 		public override void VisitGroupJoinClause(GroupJoinClause groupJoinClause, QueryModel queryModel, int index)
 		{
 			throw new NotImplementedException();