Hibernate: Increment from a specific value

Question

I created an attribute like Integer called registration and want that, when the user is to register, the value of this registration is generated automatically and saved in mysql from a certain value(Ex: 95000) and as others will register, will be the last used registration + 1 (95001, 95002...).

You can do that with Hibernate?

Answer 1

I’m not sure I understand, but come on. I will assume that you already have a running Mysql database and that you will need to recover the last (highest) enrollment used and use it to determine which registration number of the new registration you are creating.

First of all, use a query to retrieve the values of the registrations and compare them to each other to find out which is the biggest.

private int getUltimaMatricula() {
  EntityManager em = createEntityManagerFactory();
  em.getTransaction().begin();
    Query q = em.createQuery("SELECT t.coluna1 from tabela t where t.campo1 = :campo1");

    // campo1 e o que voce ira utilizar para recuperar as matriculas, utilizando jpql 
    // neste caso.
    q.setParameter("campo1", campo1);

    List<Integer> result = q.getResultList();

  int maiorNumero = Integer.MIN_VALUE;

  for(i=0; i<result.size(); i++){
    if (result.get(i) > maiorNumero)
      maiorNumero = result.get(i);
  }

  em.getTransaction().commit();
  em.close();

  return maiorValor;
}

After that, call this method inside your "persist" method or something of the type and use the number returned +1 to determine the number of the new enrollment.

Any questions, comment here.

Answer 2

I got it! I followed your idea and I did so:

private void gerarMatricula(Aluno a) {

    session = HibernateUtil.getSessionFactory().openSession();
    transaction = session.beginTransaction();
    query = session.createQuery("select matricula from Aluno");

    List<Integer> result = query.list();
    if (result.isEmpty()) {
        a.setMatricula(45100); //O primeiro aluno cadastrado receberá a matricula 45100, 

    } else{
        int maiorNumero = Integer.MIN_VALUE;

        for (int i = 0; i < result.size(); i++) {
            if (result.get(i) > maiorNumero)
                maiorNumero = result.get(i);

        }
        a.setMatricula(maiorNumero + 1);
    }


}

Then I called this method in my "persist":

public void create(Aluno a) throws Exception {

    session = HibernateUtil.getSessionFactory().openSession();
    transaction = session.beginTransaction();
    gerarMatricula(a);
    CriptografarSenha cs = new CriptografarSenha();
    cs.criptografia(a); //Criptografar a senha
    session.save(a);
    transaction.commit();
    session.close();

}

Thanks for the help!