Enable Relationship.attr functionality across reads and writes

pinax/api/relationships.py

@@ -5,10 +5,10 @@
 
 class Relationship(object):
 
-    def __init__(self, api_type, collection=False):
+    def __init__(self, api_type, collection=False, attr=None):
         self.api_type = api_type
         self.collection = collection
-        self.attr = None
+        self.attr = attr
 
     def resource_class(self):
         return registry.get(self.api_type)

pinax/api/resource.py

@@ -162,16 +162,17 @@ def get_attr(self, attr):
         return resolve_value(value)
 
     def get_relationship(self, related_name, rel):
+        attr = rel.attr if rel.attr is not None else related_name
         if rel.collection:
-            iterator = getattr(self.obj, related_name)
+            iterator = getattr(self.obj, attr)
             if not isinstance(iterator, collections.Iterable):
                 if not hasattr(iterator, "all"):
                     raise TypeError("Relationship {} must be iterable or QuerySet".format(related_name))
                 else:
                     iterator = iterator.all()
             return iterator
         else:
-            return getattr(self.obj, related_name)
+            return getattr(self.obj, attr)
 
     def set_attr(self, attr, value):
         if hasattr(self, attr.obj_attr):
@@ -191,7 +192,7 @@ def set_relationship(self, related_name, rel, value):
                         related_name, value["data"]["id"]
                     )
                 })
-            setattr(self.obj, related_name, o)
+            setattr(self.obj, f.name, o)
         else:
             # A collection can be:
             #  * ManyToManyField