EJB3.0更新表中具有相同值的字段

Question

我有一個數據庫表'MyTable'，它在更新字段'Sta​​tus'時具有觸發器。

下面是我想要做一個假碼：

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. 

長話短說，我怎樣才能做到「transfer2」的變化觸發更新，即使狀態一樣？

-Thanks

Answer 1

JPA不更新沒有更改的對象。

你可以嘗試改變其他東西（刷新），然後改回它。

您也可以使用JPQL更新查詢來更新它。

取決於你的JPA提供者，你可以強迫它更新沒有改變的字段，但這會導致非常糟糕的性能。

Answer 2

能否請您嘗試更新enity並提交事務，而不使用合併。

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礎數據庫。您的待處理查詢應發送到數據庫，但您仍可以完全回滾。