I agree that it makes sense to require a ``Model`` instance for it to work but I feel like we are breaking encapsulation  in a bad way by directly accessing ``self._fields`` (even though it is another library method that we can probably easily change if we change ``Model``). By modifying ``Model`` so it offers an iterator to the fields or by just using ``Model.iter(include_serializables=False)`` would feel cleaner in my opinion and more robust.