持久后更新JPA Container受管实体 [英] JPA Container managed entity update after persist

问题描述

您好，我在JPA中自动生成实体的主键时遇到问题.我正在坚持该实体并尝试从中获取id值，但是即使我正在执行冲洗操作，它也会返回null.我正在使用最新的glassfish，JPA，netbeans，EJB 3

Hello I am having problem with auto generated primary key of entity in JPA. I am persisting the entity and trying to get the id value out of it, but it returns null even though I am doing flush. I am using latest glassfish, JPA, netbeans, EJB 3

public class CatchesEntity implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;
    (...)




    @PersistenceContext(unitName = "DBF")
    private EntityManager em;

    (...)
    public void randomMethod()
    {
         CatchesEntity catchEntity = new CatchesEntity();
         em.persist(catchEntity);
         em.flush();
         System.out.println("CATCH ID: "+catchEntity.getId());

我得到NULL

推荐答案

调用flush()会将大多数指令发送到DB，但不会发送在commit()上生成的INSERT命令.有关更多信息，请参见此问题.

Calling flush() will send most instructions to the DB, but not the INSERTcommands that are generated on commit(). See this question for more info.

您似乎正在使用容器管理的事务，因此通常在方法返回时执行提交.

You seem to be working with container-managed transactions, so in general the commit will be performed when the method returns.

如果要在方法内强制执行提交，则可以在bean或一个方法上禁用CMT并使用UserTransaction:

If you want to force a commit inside a method, you can disable CMT either on the bean or on the one method and use a UserTransaction:

tx.begin();
...
em.persist();
tx.commit();

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