Hibernate5: how to get Root<Long> for a record-count query?

Question

I have this code

final Session session = sessionFactory.getCurrentSession();
final CriteriaBuilder builder = sessionFactory.getCriteriaBuilder();
final CriteriaQuery<ListingDetailBaseDto> criteria = builder.createQuery(ListingDetailBaseDto.class);
final Root<ListingDetailBaseDto> root = criteria.from(ListingDetailBaseDto.class);

...

public int countRecords() {
    final CriteriaQuery<Long> countingQuery = builder.createQuery(Long.class);
    countingQuery.select(countingQuery.from(Long.class));
    countingQuery.select(builder.count(root));
    final Query<Long> query = session.createQuery(countingQuery);
    return query.getSingleResult().intValue();
}       

It says Long is not a valid entity. So I remove line 3,

public int countRecords() {
    final CriteriaQuery<Long> countingQuery = builder.createQuery(Long.class);
    countingQuery.select(builder.count(root));
    final Query<Long> query = session.createQuery(countingQuery);
    return query.getSingleResult().intValue();
}   

And then the error becomes: No criteria query roots were specified

How can I get this simple record count???

Answer 1

Thanks @O.Badr for asking about root, that got me looking a little more closely at that part of the code.

The problem was caused by using root from a different CriteriaQuery object.

Fixed code:

public int countRecords() {
    final CriteriaQuery<Long> countingQuery = builder.createQuery(Long.class);
    countingQuery.select(builder.count(countingQuery.from(ListingDetailBaseDto.class)));
    final Query<Long> query = session.createQuery(countingQuery);
    return query.getSingleResult().intValue();
}