Retrieve an object identifier from the given record; if it is an
        alien class, and the type is provided, then use duck typing to get the
        corresponding fields of the alien class.

def record_id(self, record, type_=None, selector=None):
        """Retrieve an object identifier from the given record; if it is an
        alien class, and the type is provided, then use duck typing to get the
        corresponding fields of the alien class."""
        pk = record_id(record, type_, selector, self.normalize_object_slot)
        return pk