Resolve AliasedClass when determining owning class of association proxy

Fixed bug where the association proxy would inadvertently link itself
to an :class:`.AliasedClass` object if it were called first with
the :class:`.AliasedClass` as a parent, causing errors upon subsequent
usage.

Change-Id: I9161bab67766bb75d73ca54d712ad1cad6de40dc
Fixes: #4116

1 files changed, 12 insertions, 1 deletions

diff --git a/lib/sqlalchemy/ext/associationproxy.py b/lib/sqlalchemy/ext/associationproxy.py
index 16a4f3540..c0dbb538e 100644
--- a/lib/sqlalchemy/ext/associationproxy.py
+++ b/lib/sqlalchemy/ext/associationproxy.py
@@ -19,6 +19,7 @@ import weakref
 from .. import exc, orm, util
 from ..orm import collections, interfaces
 from ..sql import not_, or_
+from .. import inspect
 
 
 def association_proxy(target_collection, attr, **kw):
@@ -245,7 +246,17 @@ class AssociationProxy(interfaces.InspectionAttrInfo):
 
     def __get__(self, obj, class_):
         if self.owning_class is None:
-            self.owning_class = class_ and class_ or type(obj)
+            try:
+                insp = inspect(class_)
+            except exc.NoInspectionAvailable:
+                pass
+            else:
+                if hasattr(insp, 'mapper'):
+                    self.owning_class = insp.mapper.class_
+
+            if self.owning_class is None:
+                self.owning_class = type(obj)
+
         if obj is None:
             return self