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JPA 2.1: Programmatic Named Queries


JPA 2.1: Programmatic Named Queries

In JPA 2.0 or the early version, you can define a named query by add a @NamedQueryannotation on the entity class.
JPA 2.1 brings a new programmatic approach to create a named query dynamically.
@Startup
@Singleton
public class ApplicationInitializer {
    
    @PersistenceContext
    EntityManager em;
    
    @PostConstruct
    public void postConstruct(){
        System.out.println("@@@application is iniitlized...");
        Query query = em.createQuery("select count(vu)from Post p join treat(p.comments  as VoteUp) vu where p.id=:id");     
        em.getEntityManagerFactory().addNamedQuery(Constants.NQ_COUNT_VOTE_UP, query);
    }
    
}
In the above the codes, use a @Singleton EJB to create the named queries at EJB@Startup stage.
Replace the query string in the voteUp method with the following content.
private void fetchVoteUp() {

 this.voteDown = ((Long) (em.createNamedQuery(Constants.NQ_COUNT_VOTE_UP)
  .setParameter("id", this.id)
  .getSingleResult())).intValue();
}
The sample codes are hosted on my github.com account, check out and play it yourself.
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