JPA Criteria Subquery on JoinTable - jpa

Question

How do I create an efficient JPA Criteria query to select a list of entities only if they exist in a join table? For example take the following three tables:
create table user (user_id int, lastname varchar(64));
create table workgroup (workgroup_id int, name varchar(64));
create table user_workgroup (user_id int, workgroup_id int); -- Join Table
The query in question (what I want JPA to produce) is:
select * from user where user_id in (select user_id from user_workgroup where workgroup_id = ?);
The following Criteria query will produce a similar result, but with two joins:
CriteriaBuilder cb = getEntityManager().getCriteriaBuilder();
CriteriaQuery<User> cq = cb.createQuery(User.class);
Root<User> root = cq.from(User.class);
cq.select(root);
Subquery<Long> subquery = cq.subquery(Long.class);
Root<User> subroot = subquery.from(User.class);
subquery.select(subroot.<Long>get("userId"));
Join<User, Workgroup> workgroupList = subroot.join("workgroupList");
subquery.where(cb.equal(workgroupList.get("workgroupId"), ?));
cq.where(cb.in(root.get("userId")).value(subquery));
getEntityManager().createQuery(cq).getResultList();
The fundamental problem seems to be that I'm using the #JoinTable annotation for the USER_WORKGROUP join table instead of a separate #Entity for the join table so it doesn't seem I can use USER_WORKGROUP as a Root in a criteria query.
Here are the entity classes:
#Entity
public class User {
#Id
#Column(name = "USER_ID")
private Long userId;
#Column(name = "LASTNAME")
private String lastname;
#ManyToMany(mappedBy = "userList")
private List<Workgroup> workgroupList;
}
#Entity
public class Workgroup {
#Id
#Column(name = "WORKGROUP_ID")
private Long workgroupId;
#Column(name = "NAME")
private String name;
#JoinTable(name = "USER_WORKGROUP", joinColumns = {
#JoinColumn(name = "WORKGROUP_ID", referencedColumnName = "WORKGROUP_ID", nullable = false)}, inverseJoinColumns = {
#JoinColumn(name = "USER_ID", referencedColumnName = "USER_ID", nullable = false)})
#ManyToMany
private List<User> userList;
}

Answer 1

As far as I know, JPA essentially ignores the join table. The JPQL that you do would be
select distinct u from user u join u.workgroupList wg where wg.name = :wgName
for the Criteria query, you should be able to do:
Criteria c = session.createCriteria(User.class, "u");
c.createAlias("u.workgroupList", "wg");
c.add(Restrictions.eq("wg.name", groupName));
c.setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY);
there's no need to worry about the middle join table.