SubQuery in a CriteriaQuery

I have the abstract class Entity and these two Entities Role and User which extends from Entity:

@Entity@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public abstract class Entity {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
protected long id = 0; }
@Entity
public class Role extends Entity{
@Column(name = "NAME", unique = true, nullable = false)
private String name;
}
@Entity
public class User extends Entity{
@Column(name = "ABBREVIATION", unique = true, nullable = false)
private String abbreviation;
//The user can have several roles
@ManyToMany
@JoinTable(
name = "USER_ROLE",
joinColumns = @JoinColumn(name = "USER_ID"),
inverseJoinColumns = @JoinColumn(name = "ROLE_ID"))
private Set<Role> roles = new HashSet<>();
}

Now when I click on a role, I want the abbreviations of the users to be displayed.
The native query for it is:

query = em.createNativeQuery("SELECT ABBREVIATION FROM dbtest.user WHERE ID IN"
+ " (SELECT USER_ID FROM dbtest.user_role WHERE ROLE_ID = " + role.getId() + ")");

i have now created a criteria query of it, which always gives me an empty list.

CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<Role> cq = cb.createQuery(Role.class);
Root<User> root = cq.from(User.class);
Subquery subquery = cq.subquery(Role.class);
Root subfrom = subquery.from(Role.class);
subquery.select(subfrom.get(Role_.id));
subquery.where(cb.equal(subfrom.get(Role_.id), role.getId()));
cq.multiselect(root.get(User_.abbreviation));
cq.where(cb.equal(root.get(User_.id), subquery));
query = em.createQuery(cq);
return query.getResultList();

What is here wrong? Can anyone help ?

First of all, set the correct types:

CriteriaBuilder cb = em.getCriteriaBuilder();
//CriteriaQuery<Role> cq = cb.createQuery(Role.class);
//The type of the data returned in multiselect.
CriteriaQuery<String> cq = cb.createQuery(String.class);
Root<User> root = cq.from(User.class);
//Add to compare
Join<User,Role> joinRole = root.join(User_.roles,JoinType.Inner);
//The type of the data returned in select.
//Subquery subquery = cq.subquery(Role.class);
Subquery<Long> subquery = cq.subquery(Long.class);
//Root subfrom = subquery.from(Role.class);
//We set the data type in the Root
Root<Role> subfrom = subquery.from(Role.class);
subquery.select(subfrom.get(Role_.id));
subquery.where(cb.equal(subfrom.get(Role_.id), role.getId()));
cq.multiselect(root.get(User_.abbreviation));
//cq.where(cb.equal(root.get(User_.id), subquery));
//To use in the where subquery, call the getSelection () method
cq.where(cb.equal(root.get(User_.id), subquery.getSelection()));
query = em.createQuery(cq);
return query.getResultList();

Also, the where of the main query is an in not an equals, change this

cq.where(cb.equal(root.get(User_.id), subquery.getSelection()));

by this

cq.where(joinRole.get(Role_.id).in(subquery.getSelection()));

CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<Role> cq = cb.createQuery(Role.class);
Root<User> root = cq.from(User.class);
Subquery<Long> subquery = cq.subquery(Long.class);
Root<Role> subqueryRoot = subquery.from(Role.class);
Predicate subqueryPredicate = 
cb.equal(subqueryRoot.get(Role_.id), role.getId());
//!!! I suspect here you have to select USER_ID, but Role entity does not contain such field        
subquery.select(subqueryRoot.get(Role_.id)) 
.where(subqueryPredicate); 
Predicate queryPredicate = cb.in(root.get(User_.id)).value(subquery); 
cq.multiselect(root.get(User_.abbreviation)).where(queryPredicate);