Add test and retroactive changelog for issue 4040

Fixes: #4040
Change-Id: I707c1cd2708a37102ad8184bec21be35cb6242d7

2 files changed, 6 insertions, 1 deletions

diff --git a/lib/sqlalchemy/orm/session.py b/lib/sqlalchemy/orm/session.py
index 2c7fd86d2..6c5553939 100644
--- a/lib/sqlalchemy/orm/session.py
+++ b/lib/sqlalchemy/orm/session.py
@@ -2316,7 +2316,8 @@ class Session(_SessionClassMethods):
 
             is_persistent_orphan = is_orphan and state.has_identity
 
-            if is_orphan and not is_persistent_orphan and state._orphaned_outside_of_session:
+            if is_orphan and not is_persistent_orphan and \
+                    state._orphaned_outside_of_session:
                 self._expunge_states([state])
             else:
                 _reg = flush_context.register_object(
diff --git a/lib/sqlalchemy/orm/unitofwork.py b/lib/sqlalchemy/orm/unitofwork.py
index 669fed618..ae5cee8d2 100644
--- a/lib/sqlalchemy/orm/unitofwork.py
+++ b/lib/sqlalchemy/orm/unitofwork.py
@@ -69,6 +69,10 @@ def track_cascade_events(descriptor, prop):
             if sess and item_state in sess._new:
                 sess.expunge(item)
             else:
+                # the related item may or may not itself be in a
+                # Session, however the parent for which we are catching
+                # the event is not in a session, so memoize this on the
+                # item
                 item_state._orphaned_outside_of_session = True
 
     def set_(state, newvalue, oldvalue, initiator):