From 378e86124b598f2773cf124beab853ad63b71ee9 Mon Sep 17 00:00:00 2001
From: Mike Bayer <mike_mp@zzzcomputing.com>
Date: Sat, 28 Jan 2012 10:45:23 -0500
Subject: [PATCH] - [bug] Fixed regression from 0.7.4 whereby using an already
 instrumented column from a superclass as "polymorphic_on" failed to resolve
 the underlying Column.  [ticket:2345]

---
 CHANGES                      |  5 +++++
 lib/sqlalchemy/orm/mapper.py |  2 +-
 test/ext/test_declarative.py | 19 ++++++++++++++++++-
 3 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/CHANGES b/CHANGES
index 7c3c6b9f7e..0c42b1f783 100644
--- a/CHANGES
+++ b/CHANGES
@@ -16,6 +16,11 @@ CHANGES
     restore_snapshot() is called a second time,
     discarding those changes. [ticket:2389]
 
+  - [bug] Fixed regression from 0.7.4 whereby
+    using an already instrumented column from a
+    superclass as "polymorphic_on" failed to resolve
+    the underlying Column.  [ticket:2345]
+
   - [feature] Added "class_registry" argument to
     declarative_base().  Allows two or more declarative
     bases to share the same registry of class names.
diff --git a/lib/sqlalchemy/orm/mapper.py b/lib/sqlalchemy/orm/mapper.py
index 13b5b3e471..4c952c1fd5 100644
--- a/lib/sqlalchemy/orm/mapper.py
+++ b/lib/sqlalchemy/orm/mapper.py
@@ -128,7 +128,7 @@ class Mapper(object):
         self.batch = batch
         self.eager_defaults = eager_defaults
         self.column_prefix = column_prefix
-        self.polymorphic_on = polymorphic_on
+        self.polymorphic_on = expression._clause_element_as_expr(polymorphic_on)
         self._dependency_processors = []
         self.validators = util.immutabledict()
         self.passive_updates = passive_updates
diff --git a/test/ext/test_declarative.py b/test/ext/test_declarative.py
index 3069c2bfec..69042b5c84 100644
--- a/test/ext/test_declarative.py
+++ b/test/ext/test_declarative.py
@@ -1,6 +1,6 @@
 
 from test.lib.testing import eq_, assert_raises, \
-    assert_raises_message
+    assert_raises_message, is_
 from sqlalchemy.ext import declarative as decl
 from sqlalchemy import exc
 import sqlalchemy as sa
@@ -1855,6 +1855,23 @@ class DeclarativeInheritanceTest(DeclarativeTestBase):
         eq_(sess.query(Engineer).filter_by(primary_language='cobol'
             ).one(), Engineer(name='vlad', primary_language='cobol'))
 
+    def test_polymorphic_on_converted_from_inst(self):
+        class A(Base):
+            __tablename__ = 'A'
+            id = Column(Integer, primary_key=True)
+            discriminator = Column(String)
+
+            @declared_attr
+            def __mapper_args__(cls):
+                return {
+                    'polymorphic_identity': cls.__name__,
+                    'polymorphic_on': cls.discriminator
+                }
+
+        class B(A):
+            pass
+        is_(B.__mapper__.polymorphic_on, A.__table__.c.discriminator)
+
     def test_add_deferred(self):
 
         class Person(Base, fixtures.ComparableEntity):
-- 
2.47.2