from tortoise import BaseDBAsyncClient

async def upgrade(db: BaseDBAsyncClient) -> str:
    return """
        ALTER TABLE "users" ADD "parent_id" UUID;
        ALTER TABLE "users" ADD CONSTRAINT "fk_users_users_parent" FOREIGN KEY ("parent_id") REFERENCES "users" ("id") ON DELETE SET NULL;"""

async def downgrade(db: BaseDBAsyncClient) -> str:
    return """
        ALTER TABLE "users" DROP CONSTRAINT "fk_users_users_parent";
        ALTER TABLE "users" DROP COLUMN "parent_id";"""