JPA 2 Criteria Fetch 路径导航

Question

使用 JPA 2 Criteria Join 方法，我可以执行以下操作：

     //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();

我怎样才能用 fetch 方法做同样的事情，我希望 Fetch 接口有路径导航的 get 方法，但它没有：

     //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();

根据 Hiberante 文档，fetch 返回一个错误的 Join 对象。 http://docs.jboss.org/hibernate/stable/entitymanager/reference/en/html/querycriteria.html#querycriteria-from-fetch

原文由 Alfredo Osorio 发布，翻译遵循 CC BY-SA 4.0 许可协议

Answer 1

同意您关于该方法的看法，以及您希望它允许您所说的事实。另一种选择是

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

即做一个 join() ，为它添加一个 fetch() ，然后使用连接。这是不合逻辑的，只会增加 JPA Criteria 的不雅本质，但无论如何，应该是一种解决方法

原文由 DataNucleus 发布，翻译遵循 CC BY-SA 3.0 许可协议

Answer 2

它适用于我使用 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();

当然，它可能会破坏可移植性，但在我们的例子中，我们一直在使用其他 hibernate 的独有功能。

*这很奇怪，因为休眠文档没有显示这个例子。

要掌握它，请查看此界面。

 /*
 * 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);
}

原文由 Eduardo Fabricio 发布，翻译遵循 CC BY-SA 3.0 许可协议