JPA sequence for serial number

Question

Hello,
I wonder is there a clean (or native) way to generate sequence for a table, to use it as a serial number. It needs to be consecutive (1, 2, 3 ...etc), and avoid any possible race/transaction issues(if multiple user try to persist same time). It doesn't require to be the primary key.

   @Id
    private Long id;

    private Long serialNumber;

thanks.

Answer 1

@id @GeneratedValue(strategy=IDENTITY) ?

Answer 2

@SequenceGenerator

http://wiki.eclipse.org/EclipseLink/Examples/JPA/PrimaryKey#Using_Sequence_Objects

Answer 3

I wonder is there a clean (or native) way to generate sequence for a table, to use it as a serial number.

To my knowledge, no, not for a non Id field.

But you could use a dedicated entity with the appropriate generator strategy and persist a new instance when required to get the next id from it.

Another option would be to simulate a TABLE generator strategy and to use native SQL to read the next id from it and increment it.

Answer 4

DataNucleus supports use of @GeneratedValue on non Id fields.