- backref remove object operation doesn't fail if the other-side

collection doesn't contain the item, supports noload collections
[ticket:813]

1 files changed, 7 insertions, 1 deletions

diff --git a/lib/sqlalchemy/orm/attributes.py b/lib/sqlalchemy/orm/attributes.py
index 714b00376..4b64d52e3 100644
--- a/lib/sqlalchemy/orm/attributes.py
+++ b/lib/sqlalchemy/orm/attributes.py
@@ -520,7 +520,13 @@ class GenericBackrefExtension(interfaces.AttributeExtension):
         if oldchild is child:
             return
         if oldchild is not None:
-            getattr(oldchild.__class__, self.key).impl.remove(oldchild._state, obj, initiator)
+            # With lazy=None, there's no guarantee that the full collection is
+            # present when updating via a backref.
+            impl = getattr(oldchild.__class__, self.key).impl
+            try:                
+                impl.remove(oldchild._state, obj, initiator)
+            except (ValueError, KeyError, IndexError):
+                pass
         if child is not None:
             getattr(child.__class__, self.key).impl.append(child._state, obj, initiator)