How can I build a JPA query to count the number of results of an arbitrary CriteriaQuery?

Question

I have an arbitrary JPA criteria query. I would like to know how many results that query would produce without transferring all the results from the database.

So basically I would like to create a query

select count(*) from (<the arbitrary criteria query>)

The problem is that either I don't know how to create a SubQuery from the original CriteriaQuery when implementing this like:

CriteriaQuery<Integer> countQuery = criteriaBuilder.createQuery(Integer.class);
criteriaBuilder.count(criteriaQuery);

Or I'm missing another way to implement it.

How can I do this using JPA?

Edit:
This is not a duplicate of How do I count the number of rows returned by subquery?, because I already have a CriteriaQuery instance at hand, that I would like to incorporate into a new query or modify. The other question is about crafting a query from scratch. The point this question is about is how to use the CriteriaQuery instance I already have at hand.

Answer 1

It is not possible to use a CriteriaQuery as a Subquery.

One way to count the number of rows is to use the getResultList() method.

return criteriaBuilder.createQuery(criteriaQuery).getResultList().size()

In my opinion, this is not an optimal solution, but works when you expect small result list. Otherwise you need to rewrite your existing CriteriaQuery as explained here.