JPQL: inner join with group by

Question

I'm trying to retrieve data from database using criteriabuilder. It's working great, query is almost perfect... almost. Unfortunately Java don't want me to use group by or distinct as a result of my query. How to make Java retrieve only unique records? My code is here:

List<Documentation> documentationList = new ArrayList<>();
DatabaseConnector dc = new DatabaseConnector();
List<Predicate> criteria = new ArrayList<Predicate>();
EntityManager em = dc.getEntityManager();
CriteriaBuilder builder = em.getCriteriaBuilder();

CriteriaQuery<Documentation> select = builder.createQuery(Documentation.class);
Root<Documentation> u = select.from(Documentation.class);
Join<Documentation, DocumentationUser> du = u.join("documentationUserCollection",     JoinType.INNER);

javax.persistence.Query q = em.createQuery(select);
select.groupBy(u.<String>get("documentationId"));
select.distinct(true);

documentationList = q.setMaxResults(pageSize).setFirstResult(first).getResultList();

Answer 1

Try swapping 2 lines lower the line that creates the query:

select.groupBy(u.<String>get("documentationId"));
select.distinct(true);

javax.persistence.Query q = em.createQuery(select);