saga 中补偿业务的实现。

你好：
我看demo 中saga的例子是扣减库存，大概总结下来是：
transaction 1: set amount = amount+1 where id = 1;
transaction 2: set amount = amount +2 where id = 1;
当transaction 1 发生错误，需要补偿的时候:业务端 写个方法是: set amount = amount-1 where id = 1;
当transaction 2 发生错误，需要补偿的时候:业务端 写个方法是: set amount = amount-2 where id = 1;
这是正确的。
如果换成字符串好像就不对了，例如：
transaction 1: set name = 'n1' where id = 1;
transaction 2: set name = 'n2' where id = 1;
当transaction 1 发生错误，需要补偿的时候:业务端 写个方法是: set name = null where id = 1;
当 transaction 2 补偿的时候 set name = 'n1' where id = 1。最后name 变成了 n1 了。

No file, test, or entry point is named. First locate the Saga sample that demonstrates compensation, then clarify the expected behavior for string updates; done should include an agreed compensation design and a covering sample or test.

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