- Adjustment to attribute mechanics concerning when a value is

implicitly initialized to None via first access; this action,
which has always resulted in a population of the attribute,
now emits an attribute event just like any other attribute set
operation and generates the same kind of history as one.  Additionally,
many mapper internal operations will no longer implicitly generate
these "None" values when various never-set attributes are checked.
These are subtle behavioral fixes to attribute mechanics which provide
a better solution to the problem of :ticket:`3060`, which also
involves recognition of attributes explicitly set to ``None``
vs. attributes that were never set.
fixes #3061

1 files changed, 2 insertions, 3 deletions

diff --git a/lib/sqlalchemy/orm/unitofwork.py b/lib/sqlalchemy/orm/unitofwork.py
index 2964705a2..3ef2b2edf 100644
--- a/lib/sqlalchemy/orm/unitofwork.py
+++ b/lib/sqlalchemy/orm/unitofwork.py
@@ -86,9 +86,8 @@ def track_cascade_events(descriptor, prop):
                     not sess._contains_state(newvalue_state):
                     sess._save_or_update_state(newvalue_state)
 
-            if oldvalue is not None and \
-                oldvalue is not attributes.PASSIVE_NO_RESULT and \
-                prop._cascade.delete_orphan:
+            if oldvalue not in orm_util._none_tuple and \
+                    prop._cascade.delete_orphan:
                 # possible to reach here with attributes.NEVER_SET ?
                 oldvalue_state = attributes.instance_state(oldvalue)