JPA 2 Criteria Fetch Path Navigation

Question

With JPA 2 Criteria Join method I can do the following:

    //Join Example (default inner join)
    int age = 25;
    CriteriaBuilder cb = entityManager.getCriteriaBuilder();
    CriteriaQuery<Team> c = cb.createQuery(Team.class);
    Root<Team> t = c.from(Team.class);
    Join<Team, Player> p = t.join(Team_.players);
    c.select(t).where(cb.equal(p.get(Player_.age), age));
    TypedQuery<Team> q = entityManager.createQuery(c);
    List<Team> result = q.getResultList();

How can I do the same with fetch method, I expected that Fetch interface had get method for path navigation but it doesn't:

    //Fetch Join Example

    int age = 25;
    CriteriaBuilder cb = entityManager.getCriteriaBuilder();
    CriteriaQuery<Team> cq = cb.createQuery(Team.class);
    Root<Team> t = cq.from(Team.class);
    Fetch<Team,Player> p = t.fetch(Team_.players);
    cq.where(cb.equal(p.get(Player_.age), age)); //This leads to compilation error there is no such method get in interface Fetch
    TypedQuery<Team> q = entityManager.createQuery(cq);
    List<Team> result = q.getResultList();

According to Hiberante Documentation fetch returns a Join object which is wrong. http://docs.jboss.org/hibernate/stable/entitymanager/reference/en/html/querycriteria.html#querycriteria-from-fetch

Answer 1

Agree with you about that method, and the fact that you would expect it to allow what you say. Another option would be

Join<Team, Player> p = t.join(Team_.players);
t.fetch(Team_.players);
c.select(t).where(cb.equal(p.get(Player_.age), age));

i.e do a join(), add a fetch() for it, and then make use of the join. This is illogical and only adds to the inelegant nature of JPA Criteria, but anyway, ought to be a workaround

Answer 2

It Works for me using Hibernate Provider.

//Join Example (default inner join)

    int age = 25;
    CriteriaBuilder cb = entityManager.getCriteriaBuilder();
    CriteriaQuery<Team> c = cb.createQuery(Team.class);
    Root<Team> t = c.from(Team.class);

    // Join<Team, Player> p = t.join(Team_.players); 
    Join<Team, Player> p = (Join<Team, Player>)t.fetch(Team_.players); 

    c.select(t).where(cb.equal(p.get(Player_.age), age));
    TypedQuery<Team> q = entityManager.createQuery(c);
    List<Team> result = q.getResultList();

Certainly, it could broken the portability, but in our case we have been using others hibernate's exclusive features.

*It is very strange because the hibernate documentation doesn't show this example.

To grasp it look at this interface.

/*
 * Hibernate, Relational Persistence for Idiomatic Java
 *
 * Copyright (c) 2010, Red Hat Inc. or third-party contributors as
 * indicated by the @author tags or express copyright attribution
 * statements applied by the authors.  All third-party contributions are
 * distributed under license by Red Hat Inc.
 *
 * This copyrighted material is made available to anyone wishing to use, modify,
 * copy, or redistribute it subject to the terms and conditions of the GNU
 * Lesser General Public License, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License
 * for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this distribution; if not, write to:
 * Free Software Foundation, Inc.
 * 51 Franklin Street, Fifth Floor
 * Boston, MA  02110-1301  USA
 */
package org.hibernate.ejb.criteria;

import javax.persistence.criteria.Fetch;
import javax.persistence.criteria.Join;

/**
 * Consolidates the {@link Join} and {@link Fetch} hierarchies since that is how we implement them.
 * This allows us to treat them polymorphically.
*
* @author Steve Ebersole
*/
public interface JoinImplementor<Z,X> extends Join<Z,X>, Fetch<Z,X>, FromImplementor<Z,X> {
    /**
     * {@inheritDoc}
     * <p/>
     * Refined return type
     */
    public JoinImplementor<Z,X> correlateTo(CriteriaSubqueryImpl subquery);
}

Answer 3

All you have to do is the following:

1- Do Fetch. 2- Then, go over the path to where you want.

In your case:

int age = 25;
CriteriaBuilder cb = entityManager.getCriteriaBuilder();
CriteriaQuery<Team> cq = cb.createQuery(Team.class);
Root<Team> t = cq.from(Team.class);
Fetch<Team,Player> p = t.fetch(Team_.players);
cq.where(cb.equal(t.get("player").get("age"), age));