数据在支持交易块不可见

Question

我的方法调用如下。

@TransactionAttribute(TransactionAttributeType.SUPPORTS
void M1() {
   M2();
   M3();
}

@TransactionAttribute(TransactionAttributeType.REQUIRED)    
void M2(){
   //saving x on data base
}

@TransactionAttribute(TransactionAttributeType.SUPPORTS)
void M3(){
    //accessing x from data base
}

问题是，有时值 x 在方法 M3 中不可用。

任何机构都可以说这里可能出现的问题是什么？

Answer 1

你的例子有两种情况，结果取决于事务是否已经在M1开始，让我告诉你它是如何工作的

public void M1() {
   //transaction doesn't exist now
   M2();
   //transaction context has been created and ended due to REQUIRED attribute
   M3(); 
   //now you see result in DB because it was commited in M2s transaction 
}

public void M1() {
   //transaction already exists from method which called M1
   M2(); 
   //joins the transactional context
   M3();  //gets attached to the same context
   // and now whole transaction gets commited and only now you can be sure that you can read from DB safely
}

希望对您有所帮助，解决方案也将标记M1 REQUIRED。