- Fixed a critical regression caused by :ticket:`3061` where the

NEVER_SET symbol could easily leak into a lazyload query, subsequent
to the flush of a pending object.  This would occur typically
for a many-to-one relationship that does not use a simple
"get" strategy.   The good news is that the fix improves efficiency
vs. 0.9, because we can now skip the SELECT statement entirely
when we detect NEVER_SET symbols present in the parameters; prior to
:ticket:`3061`, we couldn't discern if the None here were set or not.
fixes #3368

3 files changed, 5 insertions, 1 deletions

diff --git a/lib/sqlalchemy/orm/base.py b/lib/sqlalchemy/orm/base.py
index c259878f0..785bd09dd 100644
--- a/lib/sqlalchemy/orm/base.py
+++ b/lib/sqlalchemy/orm/base.py
@@ -181,6 +181,8 @@ NOT_EXTENSION = util.symbol(
 
     """)
 
+_never_set = frozenset([NEVER_SET])
+
 _none_set = frozenset([None, NEVER_SET, PASSIVE_NO_RESULT])
 
 _SET_DEFERRED_EXPIRED = util.symbol("SET_DEFERRED_EXPIRED")
diff --git a/lib/sqlalchemy/orm/strategies.py b/lib/sqlalchemy/orm/strategies.py
index c03e133de..5c6618686 100644
--- a/lib/sqlalchemy/orm/strategies.py
+++ b/lib/sqlalchemy/orm/strategies.py
@@ -585,6 +585,8 @@ class LazyLoader(AbstractRelationshipLoader, util.MemoizedSlots):
 
         if pending and orm_util._none_set.intersection(params.values()):
             return None
+        elif orm_util._never_set.intersection(params.values()):
+            return None
 
         q = q.filter(lazy_clause).params(params)
 
diff --git a/lib/sqlalchemy/orm/util.py b/lib/sqlalchemy/orm/util.py
index b3f3bc5fa..b9098c77c 100644
--- a/lib/sqlalchemy/orm/util.py
+++ b/lib/sqlalchemy/orm/util.py
@@ -13,7 +13,7 @@ from . import attributes
 import re
 
 from .base import instance_str, state_str, state_class_str, attribute_str, \
-    state_attribute_str, object_mapper, object_state, _none_set
+    state_attribute_str, object_mapper, object_state, _none_set, _never_set
 from .base import class_mapper, _class_to_mapper
 from .base import InspectionAttr
 from .path_registry import PathRegistry