JPA2 Criteria-API: select… in (select from where)

Question

I have the following database model:

A
aId

AB
aId
bId

B
bId
status

In a Spring data Specification, I want to return the instances of A wh

Answer 1

Select In - is an option but you could achieve same result with double join. And its easier to make such a jpa specification:
SELECT A.ID FROM A LEFT JOIN AB ON A.ID = AB.A_ID LEFT JOIN B ON AB.B_ID = B.ID WHERE B.STATUS = 'STATUS'
Method would look like this:

public static Specification<A> findB(String input) {
    return new Specification<A>() {
        @Override
        public Predicate toPredicate(Root<A> root, CriteriaQuery<?> cq, CriteriaBuilder cb) {
            Join<A,AB> AjoinAB = root.joinList(A_.AB_LIST,JoinType.LEFT);
            Join<AB,B> ABjoinB = AjoinAB.join(AB_.B,JoinType.LEFT);
            return cb.equal(ABjoinB.get(B_.NAME),input);
        }
    };
}

Or shorter

public static Specification<A> findB(String input) {
    return (Specification<A>) (root, cq, cb) -> {
        Join<A,AB> AjoinAB = root.joinList(A_.AB_LIST,JoinType.LEFT);
        Join<AB,B> ABjoinB = AjoinAB.join(AB_.B,JoinType.LEFT);
        return cb.equal(ABjoinB.get(B_.NAME),input);
    };
}

I know it's been a long time since this question arose, but I came across it when I tried to do the same. This is my solution that works and I hope it helps someone.

Entities below

@Entity
public class A {
    @Id
    private Long id;
    private String name;
    @OneToMany(mappedBy = "a")
    private List<AB> abList;
}
@Entity
public class B {
    @Id
    private Long id;
    private String status;
    @OneToMany(mappedBy = "b")
    private List<AB> abList;
}
@Entity
public class AB {
    @Id
    private Long id;
    private String name;
    @ManyToOne
    @JoinColumn(name = "a_id")
    private A a;
    @ManyToOne
    @JoinColumn(name = "b_id")
    private B b;
}

Answer 2

There are some good examples included on a previous post that address exactly what you're trying to accomplish here: jpa-2-0-criteria-api-subqueries-in-expressions.

Answer 3

The Specification that returns instances of A using Criteria API is the following:

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);
          }
        };
     }
}

Answer 4

I suppose you wanted to select "A entities from AB entities where B is of provided status":

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));