How to get the auto-increment primary key value in MySQL using Hibernate

Question

I'm using Hibernate to access MySQL, and I have a table with an auto-increment primary key.

Everytime I insert a row into the table I don't need to specify the primary key. But after I insert a new row, how can I get the relative primary key immediately using hibernate?

Or I can just use jdbc to do this?

Answer 1

When you save the hibernate entity, the id property will be populated for you. So if you have

MyThing thing = new MyThing();
...

// save the transient instance.
dao.save(thing);

// after the session flushes, thing.getId() should return the id.

I actually almost always do an assertNotNull on the id of a persisted entity in my tests to make sure the save worked.

Answer 2

Once you're persisted the object, you should be able to call getId() or whatever your @ID column is, so you could return that from your method. You could also invalidate the Hibernate first level cache and fetch it again.

However, for portability, you might want to look at using Hibernate with sequence style ID generation. This will ease the transition away from MySQL if you ever need to. Certainly, if you use this style of generator, you'll be able to get the ID immediately, because Hibernate needs to resolve the column value before it persists the object:

@Id
@GeneratedValue (generator="MY_SEQ")
@GenericGenerator( name = "MY_SEQ",
    strategy = "org.hibernate.id.enhanced.SequenceStyleGenerator",
    parameters = { 
        @Parameter(name = "sequence_name", value = "MY_SEQ"), 
        @Parameter(name = "initial_value", value = "1"), 
        @Parameter(name = "increment_size", value = "10") }
        )
@Column ( name = "id", nullable = false )
public Long getId () {

        return this.id;
    }

It's a bit more complex, but it's the kind of thing you can cut and paste, apart from changing the SEQUENCE name.