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

java jpa-2.0 criteriaquery
Sean Patrick Floyd picture Sean Patrick Floyd · May 21, 2010 · Viewed 147.1k times · Source

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 count the results of a CriteriaQuery without actually retrieving them. Is that possible, I did not find any such method, the only way would be to do this:

CriteriaBuilder cb = entityManager.getCriteriaBuilder();

CriteriaQuery<MyEntity> cq = cb
        .createQuery(MyEntityclass);

// initialize predicates here

return entityManager.createQuery(cq).getResultList().size();

And that can't be the proper way to do it...

Is there a solution?

Answer

Affe picture Affe · May 21, 2010

A query of type MyEntity is going to return MyEntity. You want a query for a Long.

CriteriaBuilder qb = entityManager.getCriteriaBuilder();
CriteriaQuery<Long> cq = qb.createQuery(Long.class);
cq.select(qb.count(cq.from(MyEntity.class)));
cq.where(/*your stuff*/);
return entityManager.createQuery(cq).getSingleResult();

Obviously you will want to build up your expression with whatever restrictions and groupings etc you skipped in the example.

Related questions

JPA Query selecting only specific columns without using Criteria Query?

Is it possible to select, say, only properties A and B from an object using a JPA query without using criteria queries? To select all properties I'd just do something like: SELECT i FROM ObjectName i WHERE i.id = 10 But …

Read More
jpa 2 hibernate limit (max results) to a CriteriaQuery

maybe it's a silly question but I cannot find the answer in the docs: How can set a limit to the CriteriaQuery using JPA2? Thanks

Read More
JPA Criteria API - How to add JOIN clause (as general sentence as possible)

I am trying to construct queries dynamically, and my next target is add JOIN clauses (I don't know how can I use the API). By now, for example, this code work for me : ... Class baseClass; ... CriteriaBuilder cb = JpaHandle.get().getCriteriaBuilder(); …

Read More