More fixed recommended by Elrond

This fixes the problem where GenericForeignKey could only be used with models
that are in the core of Mediagoblin, it now can be used with any model
that SQLAlchemy knows about, including plugins. This also fixes some small bugs
caused by incorrect ordering of params into a function.

mediagoblin/db/models.py

@@ -89,7 +89,7 @@ class GenericModelReference(Base):
 
         # Check that the field on the model is a an integer field
         pk_column = getattr(model, primary_keys[0])
-        if issubclass(Integer, pk_column):
+        if issubclass(pk_column, Integer):
             raise ValueError("Only models with integer pks can be set")
 
         # Ensure that everything has it's ID set
@@ -99,20 +99,17 @@ class GenericModelReference(Base):
         self.model_type = obj.__tablename__
 
     def _get_model_from_type(self, model_type):
-        """
-        Gets a model from a tablename (model type)
-
-        This currently only works for core models, I've not been able to find
-        this data built by SQLAlchemy, the closes I found was
-        Base._metadata.tables but that only gives me a `Table` object.
-        """
-        if getattr(self.__class__, "_TYPE_MAP", None) is None:
+        """ Gets a model from a tablename (model type) """
+        if getattr(type(self), "_TYPE_MAP", None) is None:
             # We want to build on the class (not the instance) a map of all the
             # models by the table name (type) for easy lookup, this is done on
             # the class so it can be shared between all instances
 
             # to prevent circular imports do import here
-            self._TYPE_MAP = dict(((m.__tablename__, m) for m in MODELS))
+            registry = Base._decl_class_registry
+            self._TYPE_MAP = dict(
+                ((m.__tablename__, m) for m in six.itervalues(registry))
+            )
             setattr(self.__class__, "_TYPE_MAP",  self._TYPE_MAP)
 
         return self.__class__._TYPE_MAP[model_type]
@@ -176,7 +173,7 @@ class GenericForeignKey(types.TypeDecorator):
         if gmr is None:
             gmr = GenericModelReference()
             gmr.set_object(value)
-            gmr.save()
+            gmr.save(commit=False)
 
         return gmr.id