def _serialize(self):
        """
        A helper method to build a dict of all mutable Properties of
        this object
        """
        result = { a: getattr(self, a) for a in type(self).properties
            if type(self).properties[a].mutable }

        for k, v in result.items():
            if isinstance(v, Base):
                result[k] = v.id

        return result