- Fixed issue where two same-named relationships that refer to

a base class and a concrete-inherited subclass would raise an error
if those relationships were set up using "backref", while setting up the
identical configuration using relationship() instead with the conflicting
names would succeed, as is allowed in the case of a concrete mapping.
fixes #3630

2 files changed, 16 insertions, 10 deletions

diff --git a/lib/sqlalchemy/orm/mapper.py b/lib/sqlalchemy/orm/mapper.py
index 95aa14a26..88dadcc22 100644
--- a/lib/sqlalchemy/orm/mapper.py
+++ b/lib/sqlalchemy/orm/mapper.py
@@ -1591,7 +1591,12 @@ class Mapper(InspectionAttr):
 
         if key in self._props and \
                 not isinstance(prop, properties.ColumnProperty) and \
-                not isinstance(self._props[key], properties.ColumnProperty):
+                not isinstance(
+                    self._props[key],
+                    (
+                        properties.ColumnProperty,
+                        properties.ConcreteInheritedProperty)
+                ):
             util.warn("Property %s on %s being replaced with new "
                       "property %s; the old property will be discarded" % (
                           self._props[key],
diff --git a/lib/sqlalchemy/orm/relationships.py b/lib/sqlalchemy/orm/relationships.py
index f822071c4..9b02d86e9 100644
--- a/lib/sqlalchemy/orm/relationships.py
+++ b/lib/sqlalchemy/orm/relationships.py
@@ -1817,15 +1817,16 @@ class RelationshipProperty(StrategizedProperty):
                 backref_key, kwargs = self.backref
             mapper = self.mapper.primary_mapper()
 
-            check = set(mapper.iterate_to_root()).\
-                union(mapper.self_and_descendants)
-            for m in check:
-                if m.has_property(backref_key):
-                    raise sa_exc.ArgumentError(
-                        "Error creating backref "
-                        "'%s' on relationship '%s': property of that "
-                        "name exists on mapper '%s'" %
-                        (backref_key, self, m))
+            if not mapper.concrete:
+                check = set(mapper.iterate_to_root()).\
+                    union(mapper.self_and_descendants)
+                for m in check:
+                    if m.has_property(backref_key):
+                        raise sa_exc.ArgumentError(
+                            "Error creating backref "
+                            "'%s' on relationship '%s': property of that "
+                            "name exists on mapper '%s'" %
+                            (backref_key, self, m))
 
             # determine primaryjoin/secondaryjoin for the
             # backref.  Use the one we had, so that