Method _check_fk_val

django/db/models/fields/related_descriptors.py:737–743

(self)

        do_not_call_in_templates = True

        def _check_fk_val(self):
            for field in self.field.foreign_related_fields:
                if getattr(self.instance, field.attname) is None:
                    raise ValueError(
                        f'"{self.instance!r}" needs to have a value for field '
                        f'"{field.attname}" before this relationship can be used.'
                    )

        def _apply_rel_filters(self, queryset):
            """