JPA2标准-API:选择...在(从哪里选择)

Question

我有以下数据库模型：

A
aId

AB
aId
bId

B
bId
status

在Spring数据规范中，当B.status为'X'时，我想返回A的实例。JPQL代码如下：

select a from A a where a in
     (select ab.id.a from AB ab where ab.id.b.status= :status)

这些是模型类：

@Entity
public class A {
     private Long aId;

     @OneToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL, mappedBy = "id.a")
     private Set<AB> ab;
}

@Entity
public class B {
     private Long bId;
     private String Status;

     @OneToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL, mappedBy = "id.b")
     private Set<AB> ab;
}

@Entity
public class AB {
     private ABPK id;
}

public class ABPK {
     @ManyToOne
     @JoinColumn(name="aId")
     private A a;

     @ManyToOne
     @JoinColumn(name="bId")
     private B b;
}

Spring规范中的JPA标准是什么？

public class ASpecifications {
     public static Specification<A> test(final String status) {
          return new Specification<Party>() {
          @Override
          public Predicate toPredicate(Root<A> a, CriteriaQuery<?> query, CriteriaBuilder cb) {
            return null;
          }
        };
     }
}

Answer 1

我想您想选择“A实体来自AB实体，其中B为提供状态”：

CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<A> cq = cb.createQuery(A.class);
Root<AB> ab = cq.from(AB.class);
cq.select(ab.get("id").get("a"));
cq.where(cb.equal(ab.get("id").get("b.status"), status));

Answer 2

在之前的一篇文章中包含了一些很好的例子，它们准确地解决了你在这里试图完成的事情：jpa-2-0-criteria-api-subqueries-in-expressions。

Answer 3

返回using Criteria API实例的规范如下：

public class ASpecifications {
     public static Specification<A> test(final String status) {
          return new Specification<Party>() {
          @Override
          public Predicate toPredicate(Root<A> a, CriteriaQuery<?> query, CriteriaBuilder cb) {
            Subquery<A> sq = query.subquery(A.class);
            Root<AB> ab = sq.from(AB.class);
            sq.select(ab.get(AB_.id).get(ABPK_.a));
            sq.where(cb.equal(ab.get(AB_.id).get(ABPK_.b).get(B_.status), status));

            Predicate p = cb.in(a).value(sq);
            return cb.and(p);
          }
        };
     }
}