- do a straight __subclasses__ traversal here, so that we aren't

iterating through all mappers in memory when a new event is tacked
onto an unmapped superclass, also removes the strong ref that was
breaking some GC teardown tests

1 files changed, 2 insertions, 1 deletions

diff --git a/lib/sqlalchemy/orm/util.py b/lib/sqlalchemy/orm/util.py
index dfa3ef852..43632ff13 100644
--- a/lib/sqlalchemy/orm/util.py
+++ b/lib/sqlalchemy/orm/util.py
@@ -932,7 +932,6 @@ def _attr_as_key(attr):
     else:
         return expression._column_as_key(attr)
 
-
 _state_mapper = util.dottedgetter('manager.mapper')
 
 @inspection._inspects(object)
@@ -950,6 +949,8 @@ def _inspect_mapped_object(instance):
 def _inspect_mapped_class(class_, configure=False):
     try:
         class_manager = attributes.manager_of_class(class_)
+        if not class_manager.is_mapped:
+            return None
         mapper = class_manager.mapper
         if configure and mapperlib.module._new_mappers:
             mapperlib.configure_mappers()