fix test for same mapper to use "isa"

Fixed issue in joined eager loading where an assertion fail would occur
with a particular combination of outer/inner joined eager loads in
conjunction with an inherited subclass mapper as the middle target.

Fixes: #8738
Change-Id: I4909e7518302cbb82046e0425abbbdc8eb1c0146

1 files changed, 7 insertions, 3 deletions

diff --git a/lib/sqlalchemy/orm/strategies.py b/lib/sqlalchemy/orm/strategies.py
index c381b4ba7..b65774f0a 100644
--- a/lib/sqlalchemy/orm/strategies.py
+++ b/lib/sqlalchemy/orm/strategies.py
@@ -2541,6 +2541,11 @@ class JoinedLoader(AbstractRelationshipLoader):
         self, path, join_obj, clauses, onclause, extra_criteria, splicing=False
     ):
 
+        # recursive fn to splice a nested join into an existing one.
+        # splicing=False means this is the outermost call, and it
+        # should return a value.  splicing=<from object> is the recursive
+        # form, where it can return None to indicate the end of the recursion
+
         if splicing is False:
             # first call is always handed a join object
             # from the outside
@@ -2555,7 +2560,7 @@ class JoinedLoader(AbstractRelationshipLoader):
                 splicing,
             )
         elif not isinstance(join_obj, orm_util._ORMJoin):
-            if path[-2] is splicing:
+            if path[-2].isa(splicing):
                 return orm_util._ORMJoin(
                     join_obj,
                     clauses.aliased_insp,
@@ -2566,7 +2571,6 @@ class JoinedLoader(AbstractRelationshipLoader):
                     _extra_criteria=extra_criteria,
                 )
             else:
-                # only here if splicing == True
                 return None
 
         target_join = self._splice_nested_inner_join(
@@ -2589,7 +2593,7 @@ class JoinedLoader(AbstractRelationshipLoader):
             )
             if target_join is None:
                 # should only return None when recursively called,
-                # e.g. splicing==True
+                # e.g. splicing refers to a from obj
                 assert (
                     splicing is not False
                 ), "assertion failed attempting to produce joined eager loads"