- Error message when a string arg sent to :func:`.relationship` which

doesn't resolve to a class or mapper has been corrected to work
the same way as when a non-string arg is received, which indicates
the name of the relationship which had the configurational error.
[ticket:2888]

1 files changed, 10 insertions, 12 deletions

diff --git a/lib/sqlalchemy/orm/relationships.py b/lib/sqlalchemy/orm/relationships.py
index 8296be60a..c1cf07fbe 100644
--- a/lib/sqlalchemy/orm/relationships.py
+++ b/lib/sqlalchemy/orm/relationships.py
@@ -1348,23 +1348,21 @@ class RelationshipProperty(StrategizedProperty):
         This is a lazy-initializing static attribute.
 
         """
-        if isinstance(self.argument, type):
-            mapper_ = mapperlib.class_mapper(self.argument,
-                    configure=False)
-        elif isinstance(self.argument, mapperlib.Mapper):
-            mapper_ = self.argument
-        elif util.callable(self.argument):
-
-            # accept a callable to suit various deferred-
-            # configurational schemes
+        if util.callable(self.argument) and \
+            not isinstance(self.argument, (type, mapperlib.Mapper)):
+            argument = self.argument()
+        else:
+            argument = self.argument
 
-            mapper_ = mapperlib.class_mapper(self.argument(),
+        if isinstance(argument, type):
+            mapper_ = mapperlib.class_mapper(argument,
                     configure=False)
+        elif isinstance(self.argument, mapperlib.Mapper):
+            mapper_ = argument
         else:
             raise sa_exc.ArgumentError("relationship '%s' expects "
                     "a class or a mapper argument (received: %s)"
-                    % (self.key, type(self.argument)))
-        assert isinstance(mapper_, mapperlib.Mapper), mapper_
+                    % (self.key, type(argument)))
         return mapper_
 
     @util.memoized_property