improved error message when a backref conflicts with a column-based property

diff --git a/lib/sqlalchemy/orm/properties.py b/lib/sqlalchemy/orm/properties.py
index 26717fb659fbb6bc1f6507abb8041f72bdbc9bc0..5551348747662dac6f26b75bafc101a37c055c9e 100644 (file)
--- a/lib/sqlalchemy/orm/properties.py
+++ b/lib/sqlalchemy/orm/properties.py
@@ -717,6 +717,8 @@ class BackRef(object):
             parent = prop.parent.primary_mapper()
             relation = cls(parent, prop.secondary, pj, sj, backref=prop.key, is_backref=True, **self.kwargs)
             mapper._compile_property(self.key, relation);
+        elif not isinstance(mapper.props[self.key], PropertyLoader):
+            raise exceptions.ArgumentError("Cant create backref '%s' on mapper '%s'; an incompatible property of that name already exists" % (self.key, str(mapper)))
         else:
             # else set one of us as the "backreference"
             parent = prop.parent.primary_mapper()

diff --git a/test/orm/mapper.py b/test/orm/mapper.py
index 5cf665fd415587f35421884510b71ee5e2bc58df..49b5a0cbcb8ea5cf70fea551f98901e429ded82b 100644 (file)
--- a/test/orm/mapper.py
+++ b/test/orm/mapper.py
@@ -101,6 +101,21 @@ class MapperTest(MapperSuperTest):
         finally:
             table.drop()
 
+    def testpropconflict(self):
+        """test that a backref created against an existing mapper with a property name
+        conflict raises a decent error message"""
+        mapper(Address, addresses)
+        mapper(User, users,
+            properties={
+            'addresses':relation(Address, backref='email_address')
+        })
+        try:
+            class_mapper(Address)
+            class_mapper(User)
+            assert False
+        except exceptions.ArgumentError:
+            pass
+        
     def testrefresh(self):
         mapper(User, users, properties={'addresses':relation(mapper(Address, addresses))})
         s = create_session()