Test attributes for being non-mapped column properties more closely

Fixed bug in concrete inheritance mapping where user-defined
attributes such as hybrid properties that mirror the names
of mapped attributes from sibling classes would be overwritten by
the mapper as non-accessible at the instance level.  Also
ensured that user-bound descriptors are not implicitly invoked at the class
level during the mapper configuration stage.

Change-Id: I52b84a15c296b14efeaffb72941fc941d1d52c0d
Fixes: #4188

1 files changed, 9 insertions, 0 deletions

diff --git a/lib/sqlalchemy/orm/instrumentation.py b/lib/sqlalchemy/orm/instrumentation.py
index d5422b0d0..1b839cf5c 100644
--- a/lib/sqlalchemy/orm/instrumentation.py
+++ b/lib/sqlalchemy/orm/instrumentation.py
@@ -168,6 +168,15 @@ class ClassManager(dict):
                 if isinstance(val, interfaces.InspectionAttr):
                     yield key, val
 
+    def _get_class_attr_mro(self, key, default=None):
+        """return an attribute on the class without tripping it."""
+
+        for supercls in self.class_.__mro__:
+            if key in supercls.__dict__:
+                return supercls.__dict__[key]
+        else:
+            return default
+
     def _attr_has_impl(self, key):
         """Return True if the given attribute is fully initialized.