JPA: Is there a way to return the next availble PK

if the field id inside my Entity is like this

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
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then when I persist the Entity, a unique random Id is created. Is there a way that I can retrieve the next available PK before persist

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There isn't in the spec, although some implementations may provide a means. The problem is the ID is generated by the database in some cases, whether by a sequence or a autoincrement. It's too challenging for JPA to know exactly what to do.

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Without knowing exactly what you are planning to do with the id when you have it, I found this link that may be helpful. I would write a custom sequence class that just calls the super methods to generate the id but then do what you need to do once you have it.

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In EclipseLink you can do this buy,

Number nextId = entityManager.unwrap(Session.class).getNextSequenceNumberValue(MyEntity.class);

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@Harry Pham See the Eclipselink User Guide:

http://wiki.eclipse.org/EclipseLink/UserGuide/JPA/Basic_JPA_Development/Entities/Ids/GeneratedValue

At the bottom it states what James already said. You can use the following code to obtain the next sequence number value:

long id = em.unwrap(Session.class).getNextSequenceNumberValue(Employee.class).longValue();

The Session class is in package org.eclipselink.persistence.Sessions.

But using this is eclipselink proprietary and not JPA.