了解Spring事务 - 当事务方法调用另一个事务方法时会发生什么？ [英] Understanding Spring transactions - What happens when a transactional method calls another transactional method?
问题描述
只是为了理解Spring事务的工作原理我想知道在下面的情况下会发生什么，其中一个标记为 @Transactional 的方法调用标记为<$ c $的另一个方法c> @Transactional 。
Just to understand the workings of Spring transactions I want to know what happens in the following case where one method marked as @Transactional calls another method marked as @Transactional.
假设配置使用所有默认设置。
Assume a the configuration uses all default settings.
@Service("myService")
@Transactional
public MyService{
public void myServiceMethod(){
myDAO.getSomeDBObjects();
}
}
@Repository("myDAO")
@Transactional
public MyDAOWithUsesBeyondMyService{
public void getSomeDBObjects(){...}
}
现在如果我输入 MyService。 myServiceMethod（）它显然会启动一个事务。然后，钻进 myDAO.getSomeDBObjects（）会发生什么？事务已经存在会导致没有新的交易产生，或者我是否在这里创建了两笔交易？
Now if I were to enter MyService.myServiceMethod() it would clearly start a transaction. Then, upon drilling into myDAO.getSomeDBObjects() what would happen? Would the fact that a transaction already exist cause no new transaction to be born, or am I creating two transactions here?
关于传播的文档（如下所述）似乎涵盖了这个，但我想验证我的理解，这对于我的处女大脑来说，有一点理解所有这一切。
The documentation (quoted below) on Propagation seems to cover this, but I'd like to verify my understanding, it was a little much for my virgin brain to comprehend all at once.
传播：通常，在事务范围
内执行的所有代码
都将在该事务中运行。但是，
您可以选择在
事务上下文已存在时执行
事务方法时指定
行为。
例如，代码可以在现有事务中继续运行
（
常见情况）;或者可以暂停现有的
交易并创建新的
交易。 Spring提供了EJB CMT熟悉的所有
的事务传播选项
。要阅读关于
Spring中事务
传播的语义，请参阅章节
10.5.7，事务传播。
Propagation: Typically, all code executed within a transaction scope will run in that transaction. However, you have the option of specifying the behavior in the event that a transactional method is executed when a transaction context already exists. For example, code can continue running in the existing transaction (the common case); or the existing transaction can be suspended and a new transaction created. Spring offers all of the transaction propagation options familiar from EJB CMT. To read about the semantics of transaction propagation in Spring, see Section 10.5.7, "Transaction propagation".
推荐答案
两个答案：
a）不要这样做。在服务层或dao层中使用 @Transactional ，但不能同时使用两者（服务层是通常的选择，因为您可能希望每个服务方法有一个事务）
a) don't do it. Use @Transactional in the service layer or the dao layer, but not both (the service layer is the usual choice, as you probably want one transaction per service method)
b）如果你这样做，会发生什么取决于 @Transactional <的传播属性/ code>注释，在本节中描述： 10.5.7交易传播。基本上： PROPAGATION_REQUIRED 表示两种方法都使用相同的交易，而 PROPAGATION_REQUIRES_NEW 开始新的交易。
b) if you do it, what happens depends on the propagation attribute of the @Transactional annotation and is described in this section: 10.5.7 Transaction propagation. Basically: PROPAGATION_REQUIRED means the same transaction will be used for both methods, while PROPAGATION_REQUIRES_NEW starts a new transaction.
关于您的评论：
当然我一直在阅读并且意识到，当我使用代理时，第二种方法将不会被事务代理管理，因此它就像任何其他方法调用一样。
Of course I kept reading and realized that, as I'm using proxies, this second method won't be managed by the transactional proxy, thus it's like any other method call.
在您的情况下情况并非如此（仅当两种方法都属于同一类时）。
That's not true in your situation (only if both methods were within the same class).
如果bean的方法 a 和 b ，并且 a 调用 b ，然后在实际方法而不是代理上调用 b ，因为它从代理中调用（bean不知道它是代理到外部世界）。
If a bean has methods a and b, and a calls b, then b is called on the actual method, not the proxy, because it is called from within the proxy (a bean doesn't know that it is proxied to the outside world).
proxy bean
a() --> a()
|
V
b() --> b()
但是，在您的情况下，服务会有一个注入的dao对象，这将是一个代理本身，所以你有这样的情况：
In your situation, however, a service would have an injected dao object, which would be a proxy itself, so you'd have a situation like this:
proxy bean
service a() --> a()
|
/---------/
|
V
dao b() --> b()
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