express typeorm transaction 구현

// create a new query runner
const queryRunner = dataSource.createQueryRunner();

// establish real database connection using our new query runner
await queryRunner.connect();

// lets now open a new transaction:
await queryRunner.startTransaction();

try {
    // execute some operations on this transaction:
    const email = await userDao.getEmailById(id);
  	const result = await userdao.getCart(email);

    // commit transaction now:
    await queryRunner.commitTransaction();
} catch (err) {
    // since we have errors let's rollback changes we made
    await queryRunner.rollbackTransaction();
} finally {
    // you need to release query runner which is manually created:
    // await queryRunner.release();
  	// error : Query runner already released. Cannot run queries anymore.
  	// release를 쓰면 위의 에러가 난다...
}

출처 : https://typeorm.io/transactions