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The result of the set. Criteria Subquery API

I am trying to use subqueries in an application that I am writing using APIs such as the secure type JPA 2.0, with Hibernate 3.6.1.Final as my provider. I have no problem choosing primitive types (Long, MyEntity, etc.), but I want to select multiple columns.

Here is an example of something quite reasonable. Ignore the unnecessary use of a subquery - it just means an illustration.

    EntityManager em = getEntityManager();
    CriteriaBuilder cb = em.getCriteriaBuilder();
    CriteriaQuery<Tuple> cq = cb.createTupleQuery();

    Subquery<Tuple> subQ = cq.subquery(Tuple.class);
    Expression<Long> subqCount;
    {
        Root<MyEntity> root = subQ.from(MyEntity.class);
        Path<MyEntity> filter = root.get(MyEntity.challenge);

        subqCount = cb.count(root);

        // How to select tuple?
        Selection<Tuple> tuple = cb.tuple(filter, subqCount);

                    // !! Run-time exception here
        Expression<Tuple> tupleExpr = (Expression<Tuple>) tuple; 

        // Not sure why I can't use multiSelect on a subQuery
        // #select only accepts Expression<Tuple>
        createSubQ.select(tupleExpr);

        createSubQ.groupBy(filter);
    }

    cq.multiselect(subqCount);

Although the compiler does not complain, I still get an exception at runtime.

    java.lang.ClassCastException: org.hibernate.ejb.criteria.expression.CompoundSelectionImpl cannot be cast to javax.persistence.criteria.Expression
  • Is this a bug in sleep mode, or am I doing something wrong?
  • If you cannot use multiselectin a subquery, then how can you perform groupBy?
  • If you cannot use groupByin a subquery, why is it in the API?
+5
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    SELECT ID FROM owners WHERE owners.Country = "SOUTH AFRICA"
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    CriteriaBuilder criteriaBuilder = em.getCriteriaBuilder();
    CriteriaQuery<Tuple> tupleCriteriaQuery = criteriaBuilder.createTupleQuery();

    Root<Issue> root = tupleCriteriaQuery.from(Issue.class);
    tupleCriteriaQuery = tupleCriteriaQuery.multiselect(root.get(IssueTable.COLUMN_ID));//select did not work.
    tupleCriteriaQuery = tupleCriteriaQuery.where(issueFilter.toPredicate(root, tupleCriteriaQuery, criteriaBuilder));

    List<Tuple> tupleResult = em.createQuery(tupleCriteriaQuery).getResultList();

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