In JPA 2, using a CriteriaQuery, how to count results

Question

I am rather new to JPA 2 and it\'s CriteriaBuilder / CriteriaQuery API:

CriteriaQuery javadoc

CriteriaQuery in the Java EE 6 tutorial

I would like to

Answer 1

I've sorted this out using the cb.createQuery() (without the result type parameter):

public class Blah() {

    CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
    CriteriaQuery query = criteriaBuilder.createQuery();
    Root root;
    Predicate whereClause;
    EntityManager entityManager;
    Class domainClass;

    ... Methods to create where clause ...

    public Blah(EntityManager entityManager, Class domainClass) {
        this.entityManager = entityManager;
        this.domainClass = domainClass;
        criteriaBuilder = entityManager.getCriteriaBuilder();
        query = criteriaBuilder.createQuery();
        whereClause = criteriaBuilder.equal(criteriaBuilder.literal(1), 1);
        root = query.from(domainClass);
    }

    public CriteriaQuery getQuery() {
        query.select(root);
        query.where(whereClause);
        return query;
    }

    public CriteriaQuery getQueryForCount() {
        query.select(criteriaBuilder.count(root));
        query.where(whereClause);
        return query;
    }

    public List list() {
        TypedQuery q = this.entityManager.createQuery(this.getQuery());
        return q.getResultList();
    }

    public Long count() {
        TypedQuery q = this.entityManager.createQuery(this.getQueryForCount());
        return q.getSingleResult();
    }
}

Hope it helps :)