在休眠保存对象之前从序列获取生成的ID

Question

How do I get the generated ID for an object before hibernate saves it. Here's the code:

@Id
@SequenceGenerator(name="MY_SEQ", sequenceName="MY_SEQ", allocationSize=1 )
@GeneratedValue(strategy=GenerationType.SEQUENCE, generator="MY_SEQ")
private long id;

Is there any way that I can do this without using a select on currval('MY_SEQ') ?

Thanks

Answer 1

Using the JPA @SequenceGenerator along with the legacy Hibernate identifiers will give you the SequenceHiLoGenerator that applies a HI/LO optimization algorithm anyway.

But for Sequences, the actual identifier value is applied during flush-time , so you won't get the actual value until the session gets flushed (a manual flush or the commit-time flush).

For IDENITY generator, you get the identifier generated prior to flushing, but that disables JDBC batching so it's not a silver-bullet either.

If you want full control, you need to resort to assigned identifiers and UUID surrogate keys are perfect for this job.