- Declarative locates the "inherits" class using a search

through __bases__, to skip over mixins that are local
to subclasses.

CHANGES

@@ -93,10 +93,13 @@ CHANGES
     - Fixed a recursive pickling issue in serializer, triggered
       by an EXISTS or other embedded FROM construct.
 
+    - Declarative locates the "inherits" class using a search
+      through __bases__, to skip over mixins that are local
+      to subclasses.   
+      
     - Declarative figures out joined-table inheritance primary join
       condition even if "inherits" mapper argument is given 
-      explicitly.  Allows mixins to be used with joined table
-      inheritance.
+      explicitly. 
 
     - Declarative will properly interpret the "foreign_keys" argument
       on a backref() if it's a string.

lib/sqlalchemy/ext/declarative.py

@@ -400,6 +400,7 @@ from sqlalchemy.schema import Table, Column, MetaData
 from sqlalchemy.orm import synonym as _orm_synonym, mapper, comparable_property, class_mapper
 from sqlalchemy.orm.interfaces import MapperProperty
 from sqlalchemy.orm.properties import PropertyLoader, ColumnProperty
+from sqlalchemy.orm.util import _is_mapped_class
 from sqlalchemy import util, exceptions
 from sqlalchemy.sql import util as sql_util
 
@@ -483,10 +484,10 @@ def _as_declarative(cls, classname, dict_):
             
     mapper_args = getattr(cls, '__mapper_args__', {})
     if 'inherits' not in mapper_args:
-        inherits = cls.__mro__[1]
-        inherits = cls._decl_class_registry.get(inherits.__name__, None)
-        if inherits:
-            mapper_args['inherits'] = inherits
+        for c in cls.__bases__:
+            if _is_mapped_class(c):
+                mapper_args['inherits'] = cls._decl_class_registry.get(c.__name__, None)
+                break
 
     if hasattr(cls, '__mapper_cls__'):
         mapper_cls = util.unbound_method_to_callable(cls.__mapper_cls__)

test/ext/declarative.py

@@ -768,7 +768,7 @@ class DeclarativeInheritanceTest(DeclarativeTestBase):
         
         # compile succeeds because inherit_condition is honored
         compile_mappers()
-
+    
     def test_joined(self):
         class Company(Base, ComparableEntity):
             __tablename__ = 'companies'
@@ -837,6 +837,25 @@ class DeclarativeInheritanceTest(DeclarativeTestBase):
         def go():
             assert sess.query(Person).filter(Manager.name=='dogbert').one().id
         self.assert_sql_count(testing.db, go, 1)
+
+    def test_subclass_mixin(self):
+        class Person(Base, ComparableEntity):
+            __tablename__ = 'people'
+            id = Column('id', Integer, primary_key=True)
+            name = Column('name', String(50))
+            discriminator = Column('type', String(50))
+            __mapper_args__ = {'polymorphic_on':discriminator}
+        
+        class MyMixin(object):
+            pass
+            
+        class Engineer(MyMixin, Person):
+            __tablename__ = 'engineers'
+            __mapper_args__ = {'polymorphic_identity':'engineer'}
+            id = Column('id', Integer, ForeignKey('people.id'), primary_key=True)
+            primary_language = Column('primary_language', String(50))
+            
+        assert class_mapper(Engineer).inherits is class_mapper(Person)
         
     def test_with_undefined_foreignkey(self):
         class Parent(Base):