春季 JPA。更新数据库值的正确方法

Question

我正在学习 Spring JPA 和 Hibernate。所以我遇到了一个问题。

我有这个方法

@Transactional(isolation = Isolation.REPEATABLE_READ)

public void sendMoney(Long from, Long to, Double amount) {

    WalletEntity fromWallet = walletServiceImpl.getWallet(from);

    WalletEntity toWallet = walletServiceImpl.getWallet(to);

    fromWallet.setAmount(fromWallet.getAmount() - amount);

    toWallet.setAmount(toWallet.getAmount() + amount);

    TransactionEntity transaction = new TransactionEntity();

    transaction.setAmount(amount);

    transaction.setToWallet(toWallet);

    transaction.setFromWallet(fromWallet);

    transactionRepository.saveAndFlush(transaction);

}

我想测试它并创建了这个：

@GetMapping("/send")

public void sendMoney() {

    ExecutorService executorService = Executors.newFixedThreadPool(20);

    for (int i = 0; i < 100; i++) {

        executorService.execute(() -> {

            accountServiceImpl.sendMoney(1L, 2L, 10D);

        });

    }

}

所以当我阅读 wallet 时，我得到了旧的价值，但我做了Isolation.REPEATABLE_READ. 数据库中的值当然是错误的。你能解释一下有什么问题吗？谢谢！

Answer 1

隔离级别 REPTEABLE_READ 按预期工作。你可以在这里得到一个很好的解释：Spring @Transactional - 隔离、传播但为了澄清，这是发生的事情：&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; Tx1&nbsp; &nbsp; &nbsp; Tx2&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;|&nbsp; &nbsp; &nbsp; &nbsp; |Tx1 Read Wallet 1&nbsp; &nbsp; &nbsp;100&nbsp; &nbsp; &nbsp; &nbsp;|Tx2 Read Wallet 1&nbsp; &nbsp; &nbsp; |&nbsp; &nbsp; &nbsp; &nbsp;100Tx1 Discounts 10&nbsp; &nbsp; &nbsp;100-10&nbsp; &nbsp; &nbsp;|Tx2 Discounts 10&nbsp; &nbsp; &nbsp; &nbsp;|&nbsp; &nbsp; &nbsp; 100-10Tx1 Commits&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; |&nbsp; &nbsp; &nbsp; &nbsp; |Tx2 Commits&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; |&nbsp; &nbsp; &nbsp; &nbsp; |Tx1 Read Wallet 1&nbsp; &nbsp; &nbsp; 90&nbsp; &nbsp; &nbsp; &nbsp;|Tx2 Read Wallet 2&nbsp; &nbsp; &nbsp; |&nbsp; &nbsp; &nbsp; &nbsp; 90因此，为了控制这种行为，您有两个选择：使用阻塞操作的可序列化事务级别以便一一处理（这有性能损失）实现乐观锁（第二个事务如果同时尝试修改同一个账户会抛出异常）您可以从这里开始回顾乐观锁：JPA 中的乐观锁是如何工作的？