Fixed bug whereby attribute history functions would fail

when an object we moved from "persistent" to "pending"
using the :func:`.make_transient` function, for operations
involving collection-based backrefs.
[ticket:2773]

1 files changed, 2 insertions, 2 deletions

diff --git a/lib/sqlalchemy/orm/attributes.py b/lib/sqlalchemy/orm/attributes.py
index 3eda127fd..7f1b5e58c 100644
--- a/lib/sqlalchemy/orm/attributes.py
+++ b/lib/sqlalchemy/orm/attributes.py
@@ -884,7 +884,7 @@ class CollectionAttributeImpl(AttributeImpl):
 
         if self.key in state.committed_state:
             original = state.committed_state[self.key]
-            if original is not NO_VALUE:
+            if original not in (NO_VALUE, NEVER_SET):
                 current_states = [((c is not None) and
                                     instance_state(c) or None, c)
                                     for c in current]
@@ -1326,7 +1326,7 @@ class History(History):
             return cls((), (), ())
 
         current = getattr(current, '_sa_adapter')
-        if original is NO_VALUE:
+        if original in (NO_VALUE, NEVER_SET):
             return cls(list(current), (), ())
         elif original is _NO_HISTORY:
             return cls((), list(current), ())