JPA标准选择组中具有最大值的所有实例 [英] JPA Criteria select all instances with max values in their groups

问题描述

是否可以使用JPA 2 CriteriaBuilder编写与以下查询等效的方法?

Is there a way to write with JPA 2 CriteriaBuilder the equivalent of the following query?

select * from season s1
where end = (
    select max(end)
    from season s2
    where s1.contest_id=s2.contest_id
);

在JPQL中，此查询为:

In JPQL this query is:

Select s1 from Season s1 
where s1.end = (
    select max(s2.end)
    from Season s2
    where s1.contest=s2.contest
)

推荐答案

这应该可以工作，其中contest是基本的Integer属性，或者是指向另一个非基本实体的ManyToOne属性.

This should work, with contest being either a basic Integer property, or a ManyToOne property pointing to another non-basic Entity.

EntityManger em;      //to be injected or constructed

CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<Season> cq = cb.createQuery(Season.class);
Subquery<Date> sq = cq.subquery(Date.class);
Root<Season> s1 = cq.from(Season.class);
Root<Season> s2 = sq.from(Season.class);
sq.select(cb.greatest(s2.get(Season_.end)));
sq.where(cb.equal(s2.get(Season_.contest), s1.get(Season_.contest)));
cq.where(cb.equal(s1.get(Season_.end), sq));
List<Season> result = em.createQuery(cq).getResultList();

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