Sorting on one-to-many relationship with JPA criteria API

Question

I'm having some trouble using JPA criteria API with collection references.
I have an entity called Competence that has a one-to-many relation to CompetenceName that contains names for Competence for several languages.
[Competence.java]
@OneToMany(mappedBy="competence", cascade=CascadeType.ALL, orphanRemoval=true)
private List<CompetenceName> competenceNames;
[CompetenceName.java]
@ManyToOne @JoinColumn(name = "competence_id", referencedColumnName = "id")
private Competence competence;
@ManyToOne @JoinColumn(name = "lang_id", referencedColumnName = "id")
private Language language;
@Basic @Column(name = "name", length = 50)
private String name
Now I want to load 200 Competence-entities and sort them by their name (depending on the language of the logged in user). How would this be done using the JPA Criteria API? With a normal query, I would accomplish this with
"SELECT DISTINCT c FROM Competence AS c LEFT JOIN c.competenceNames AS cn ORDER BY cn.name"
Obviously, CompetenceName could contain zero entries for a Competence, but it works anyway with a normal query. With criteria API, it would look something like:
CriteriaQuery<Competence> cq = cb.createQuery(Competence.class);
Root<Competence> competence = cq.from(Competence.class);
competence.fetch(Competence_.competenceNames);
cq.select(competence).orderBy(cb.asc(competence.get(Competence_.competenceNames).get(CompetenceName_.name)); // Doesn't work
Is this even possible to do without creating a normal query?
Edited by: 812655 on Nov 24, 2010 2:32 AM

Answer 1

// Doesn't workWhat does not work? What error do you get?
You need to use "join" to define a join.
CriteriaQuery<Competence> cq = cb.createQuery(Competence.class);
Root<Competence> competence = cq.from(Competence.class);
Join<CompetenceName> name = competence.join(Competence_.competenceNames);
cq.orderBy(cb.asc(name.get(CompetenceName_.name));
The "fetch" will do a fetch join, if you also wish to load the data in the same query.
James : http://www.eclipselink.org