- Two fixes to help prevent out-of-band columns from

being rendered in polymorphic_union inheritance
scenarios (which then causes extra tables to be
rendered in the FROM clause causing cartesian
products):
- improvements to "column adaption" for
  a->b->c inheritance situations to better
  locate columns that are related to one
  another via multiple levels of indirection,
  rather than rendering the non-adapted
  column.
- the "polymorphic discriminator" column is
  only rendered for the actual mapper being
  queried against. The column won't be
  "pulled in" from a subclass or superclass
  mapper since it's not needed.

1 files changed, 3 insertions, 3 deletions

diff --git a/lib/sqlalchemy/sql/util.py b/lib/sqlalchemy/sql/util.py
index d5f2417c2..1bd4dd857 100644
--- a/lib/sqlalchemy/sql/util.py
+++ b/lib/sqlalchemy/sql/util.py
@@ -439,12 +439,12 @@ class ClauseAdapter(visitors.ReplacingCloningVisitor):
         self.exclude = exclude
         self.equivalents = equivalents or {}
         
-    def _corresponding_column(self, col, require_embedded):
+    def _corresponding_column(self, col, require_embedded, _seen=util.EMPTY_SET):
         newcol = self.selectable.corresponding_column(col, require_embedded=require_embedded)
 
-        if not newcol and col in self.equivalents:
+        if not newcol and col in self.equivalents and col not in _seen:
             for equiv in self.equivalents[col]:
-                newcol = self.selectable.corresponding_column(equiv, require_embedded=require_embedded)
+                newcol = self._corresponding_column(equiv, require_embedded=require_embedded, _seen=_seen.union([col]))
                 if newcol:
                     return newcol
         return newcol