[eclipselink-users] Dynamically get a Count for any CriteriaQuery - is i

[Tim Hollosy <hollosyt@xxxxxxxxx>]

I'd like to start to use the new Criteria API rather than
EclipseLink's Expression API to make my code more portable. Here's the
issue that I'm running into however.
In my current toolbox, I have a dao method that can take any
ReadAllQuery and get a count query for it. This is great for paging.


My Expression API based method looks like this:

public BigDecimal getCountQuery ( Class clazz, Expression eb  ) {
if( eb == null ) {
eb = new ExpressionBuilder();
}
ReportQuery rq = new ReportQuery(clazz, eb);
rq.addCount();
rq.setShouldReturnWithoutReportQueryResult(true);
Vector reportRows = (Vector) JpaHelper.getEntityManager(
getEntityManager()).getActiveSession().executeQuery(rq);
        Integer count = null;
if (reportRows != null) {
      return  (BigDecimal) reportRows.get(0);
}
return null;
}



I took a stab at doing the same thing with a the CriteriaQuery API,
and just as an example -- this is not generic:

 CriteriaBuilder cb  = getEntityManager().getCriteriaBuilder();

              CriteriaQuery<Client> cq = cb.createQuery(Client.class);


              Root<Client> client = cq.from(Client.class);

              cq.where(cb.like(client.<String>get("lastName"),
search.getLastName()));

              List<Client> clients =
getEntityManager().createQuery(cq).getResultList();

              CriteriaQuery<Long> countQuery = cb.createQuery(Long.class);
              countQuery.select(cb.count(client));
              countQuery.where(cq.getRestriction());

              Long count =
getEntityManager().createQuery(countQuery).getSingleResult();


The first query looks great, the second query ends up like:

SELECT COUNT(ID) FROM CLIENT WHERE ((LAST_NAME LIKE ?) = ?)
and gets bound with '%whatever%', true

which is not a valid oracle query.


What I require is a way to easily get a count for any CriteriaQuery.
This is essential if you're trying to build a mature web application
in the real world.

I saw some people in hibernate's jira asking for this, and they cite a
rule in the jpa 2.0 spec saying you can't copy predicates from one
CriteriaQuery to another.

Is there really no way to do that in the current API? If so is there
some other way I can get the backing EL expression from a
CriteriaQuery so I can use my old count query, that'd be better than
nothing.

Thanks!

./tch