Question

I’m developing a J2EE 6 Web Application, using a MySql 5.02 DataBase. I’m trying to generate a hash digest of the ID, every time I create a new Entity. This is set to a column on the Table.

But well, I’m stuck on something that is apparently easy, and according with what I found googling, possible. Basically I want to retrieve the ID (Primary Key) of a newly persisted object, but whatever I try, it returns null.

The steps are follow are:

1. Create the Instance of the Entity -> userCard = new Users();
2. Setting the corresponding fields with some values.
3. Calling the persist() method of the EntityManager.

After reading some forums, I understood I had to either call flush() after persist(), or use merge() and use the returned entity to retrieve the id.

public void createAndFlush(Users users) {
    em.persist(users);
    em.flush();
}

public Integer edit(Users users) {
    return ((Users)em.merge(users)).getIdvcards();
}

None of them (among some other combinations) work, well, the Entity is successfully persisted, but the ID field returns null.

These are the correspinding annotations of the id column I want to retrieve:

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Basic(optional = false)
@Column(name = "idvcards")
private Integer idvcards;

And obviously, the column idvcards of my table is set to Auto-Increment and Primary Key.

Maybe I just need to clarify my Peristence-Management concepts, but I’d appreciate if I can get some hint to solve this basic issue.

Answer 1

Maybe is not the most elegant solution ever, but finally I succeded on retrieving the ID of the new Entity:

public Integer create(User user) {
    em.persist(users);
    em.flush();
    return (Integer) em.getEntityManagerFactory().getPersistenceUnitUtil().getIdentifier(users);
}

And well, althought is not related to the functionality, I changed the entity name to the singular form as @Bohemian suggested.