Method prepare_database_save

django/db/models/base.py:1433–1438

(self, field)

        return field_map

    def prepare_database_save(self, field):
        if not self._is_pk_set():
            raise ValueError(
                "Unsaved model instance %r cannot be used in an ORM query." % self
            )
        return getattr(self, field.remote_field.get_related_field().attname)

    def clean(self):
        """