Get or create key for the model.

        Returns
        ~~~~~~~
        (model_key, boolean) tuple

def get_or_create_model_key(self):
        """
        Get or create key for the model.

        Returns
        ~~~~~~~
        (model_key, boolean) tuple

        """
        model_cache_info = model_cache_backend.retrieve_model_cache_info(self.model._meta.db_table)
        if not model_cache_info:
            return uuid.uuid4().hex, True
        return model_cache_info.table_key, False