- Simplified the sweep of instrumentation in strategies._register_attribute

- Improved support for MapperProperty objects overriding
that of an inherited mapper for non-concrete
inheritance setups - attribute extensions won't randomly
collide with each other.  [ticket:1488]

- Added AttributeExtension to sqlalchemy.orm.__all__

3 files changed, 8 insertions, 2 deletions

diff --git a/lib/sqlalchemy/orm/__init__.py b/lib/sqlalchemy/orm/__init__.py
index 4c4ec8513..2a20b05ef 100644
--- a/lib/sqlalchemy/orm/__init__.py
+++ b/lib/sqlalchemy/orm/__init__.py
@@ -26,6 +26,7 @@ from sqlalchemy.orm.interfaces import (
      MapperExtension,
      PropComparator,
      SessionExtension,
+     AttributeExtension,
      )
 from sqlalchemy.orm.util import (
      AliasedClass as aliased,
@@ -61,6 +62,7 @@ __all__ = (
     'EXT_STOP',
     'InstrumentationManager',
     'MapperExtension',
+    'AttributeExtension',
     'Validator',
     'PropComparator',
     'Query',
diff --git a/lib/sqlalchemy/orm/mapper.py b/lib/sqlalchemy/orm/mapper.py
index d53faacf7..078056a01 100644
--- a/lib/sqlalchemy/orm/mapper.py
+++ b/lib/sqlalchemy/orm/mapper.py
@@ -649,6 +649,9 @@ class Mapper(object):
                         return self
 
                     # initialize properties on all mappers
+                    # note that _mapper_registry is unordered, which 
+                    # may randomly conceal/reveal issues related to 
+                    # the order of mapper compilation
                     for mapper in list(_mapper_registry):
                         if getattr(mapper, '_compile_failed', False):
                             raise sa_exc.InvalidRequestError("One or more mappers failed to compile.  Exception was probably "
diff --git a/lib/sqlalchemy/orm/strategies.py b/lib/sqlalchemy/orm/strategies.py
index 1da2231a3..f739fb1dd 100644
--- a/lib/sqlalchemy/orm/strategies.py
+++ b/lib/sqlalchemy/orm/strategies.py
@@ -45,9 +45,10 @@ def _register_attribute(strategy, mapper, useobject,
     
     if useobject:
         attribute_ext.append(sessionlib.UOWEventHandler(prop.key))
-
+    
     for m in mapper.polymorphic_iterator():
-        if (m is prop.parent or not m.concrete) and m.has_property(prop.key):
+        if prop is m._props.get(prop.key):
+            
             attributes.register_attribute_impl(
                 m.class_, 
                 prop.key,