def _get_parent_constraint(self, store_type: StoreType) -> str:
        """Get the appropriate foreign key constraint for the store type."""
        if store_type == StoreType.GRAPHS:
            return f"""
                CONSTRAINT fk_graph
                    FOREIGN KEY(parent_id)
                    REFERENCES {self._get_table_name("graphs")}(id)
                    ON DELETE CASCADE
            """
        else:
            return f"""
                CONSTRAINT fk_document
                    FOREIGN KEY(parent_id)
                    REFERENCES {self._get_table_name("documents")}(id)
                    ON DELETE CASCADE
            """
Get the appropriate foreign key constraint for the store type.
py/core/providers/database/graphs.py