Fixed bug in polymorphic SQL generation where multiple joined-inheritance

entities against the same base class joined to each other as well
would not track columns on the base table independently of each other if
the string of joins were more than two entities long.  Also in 0.8.2.
[ticket:2759]

Conflicts:
	doc/build/changelog/changelog_09.rst

1 files changed, 10 insertions, 5 deletions

diff --git a/lib/sqlalchemy/orm/query.py b/lib/sqlalchemy/orm/query.py
index c2ec72c51..13699316f 100644
--- a/lib/sqlalchemy/orm/query.py
+++ b/lib/sqlalchemy/orm/query.py
@@ -203,17 +203,22 @@ class Query(object):
                 self._polymorphic_adapters.pop(m.local_table, None)
 
     def _adapt_polymorphic_element(self, element):
+        if "parententity" in element._annotations:
+            search = element._annotations['parententity']
+            alias = self._polymorphic_adapters.get(search, None)
+            if alias:
+                return alias.adapt_clause(element)
+
         if isinstance(element, expression.FromClause):
             search = element
         elif hasattr(element, 'table'):
             search = element.table
         else:
-            search = None
+            return None
 
-        if search is not None:
-            alias = self._polymorphic_adapters.get(search, None)
-            if alias:
-                return alias.adapt_clause(element)
+        alias = self._polymorphic_adapters.get(search, None)
+        if alias:
+            return alias.adapt_clause(element)
 
     def _adapt_col_list(self, cols):
         return [