EJB3.0更新表中具有相同值的字段

Question

我有一个数据库表'MyTable'，它在更新字段'Sta​​tus'时具有触发器。

下面是我想要做一个假码：

MyTable table = new Mytable(); 
table.setTableId(1); 
table.setStatus ("NEW"); 
em.persist (table); //At this point the trigger did not kick in since this inserted a new record 

... 

MyTable table2 = em.find(MyTable.class, 1); 
table2.setStatus ("NEW"); 
em.merge(table2)//Even though im updating the record with the same status with the same value, i still want the trigger to kick. However the trigger is not being activated. 


... 

MyTable table3 = em.find(MyTable.class, 1); 
table3.setStatus ("OLD"); 
em.merge(table3)//The trigger is being activated here since the status is different the status value when it was inserted the first time. 

长话短说，我怎样才能做到“transfer2”的变化触发更新，即使状态一样？

-Thanks

Answer 1

JPA不更新没有更改的对象。

你可以尝试改变其他东西（刷新），然后改回它。

您也可以使用JPQL更新查询来更新它。

取决于你的JPA提供者，你可以强迫它更新没有改变的字段，但这会导致非常糟糕的性能。

Answer 2

能否请您尝试更新enity并提交事务，而不使用合并。

像

em.getTransaction().begin(); 
MyTable table2 = em.find(MyTable.class, 1); 
table2.setStatus ("NEW"); 

//em.merge(table2)//Even though im updating the record with the same status with the 
// same value, i still want the trigger to kick. However the trigger is not being activated. 
em.getTransaction().commit(); 

Answer 3

使用em.flush();同步持久化上下文的基础数据库。您的待处理查询应发送到数据库，但您仍可以完全回滚。