How to find out efficiently the auto-generated id for a new object when using JPA?

I have an attribute which is annotated with @Id. The ID is going to be generated automatically when persisting the object. That means that the ID-value is not defined before I persist the object. After persisting it, it has an ID (in the database), bu开发者_如何学运维t unfortunately the field still remains null as long as I don't reload it from the DB. is there any easy way to find out the generated id? Or better: To configure that it will be written into the field?

Thanks in advance

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The id gets assigned after the flush. Assuming the Foo entity has an id attribute annotated with the standard @Id @GeneratedValue annotations, the following code works:

Foo foo = new Foo();
//...
em.persist(foo);
em.flush();
assert foo.getId() != null;