I'm trying, as in title, to insert a subquery in select clause like in this simple SQL:
SELECT id, name, (select count(*) from item) from item
this is obviously only a mock query just to make my point. (The point would be to get the last invoice for each item returned by the query.)
I've tried this:
CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<Tuple> c = cb.createTupleQuery();
Root<Item> item= c.from(Item.class);
Subquery<Long> scount = c.subquery(Long.class);
Root<Item> sarticolo = scount.from(Item.class);
scount.select(cb.count(sitem));
c.multiselect(item.get("id"),item.get("nome"), scount);
Query q = em.createQuery(c);
q.setMaxResults(100);
List<Tuple> result = q.getResultList();
for(Tuple t: result){
System.out.println(t.get(0) + ", " + t.get(1) + ", " + t.get(2));
}
but I only get:
java.lang.IllegalStateException: Subquery cannot occur in select clause
How can I get a similar result?
It is supported in JPA 2.1 and Hibernate 5.0. You just had to add getSelection()
to the subquery argument in the multiselect
of the main query.
c.multiselect(item.get("id"),item.get("nome"), scount.getSelection());
Take a look at this working example:
CriteriaBuilder builder = em.getCriteriaBuilder();
CriteriaQuery<NotificationInfo> cq = builder.createQuery(NotificationInfo.class); //wrapper class
Root<Notification> n = cq.from(Notification.class); //root entity
//Subquery
Subquery<Long> sqSent = cq.subquery(Long.class);
Root<NotificationUser> sqSentNU = sqSent.from(NotificationUser.class);
sqSent.select(builder.count(sqSentNU));
sqSent.where(
builder.equal(sqSentNU.get(NotificationUser_.notification), n), //join subquery with main query
builder.isNotNull(sqSentNU.get(NotificationUser_.sendDate))
);
cq.select(
builder.construct(
NotificationInfo.class,
n.get(Notification_.idNotification),
n.get(Notification_.creationDate),
n.get(Notification_.suspendedDate),
n.get(Notification_.type),
n.get(Notification_.title),
n.get(Notification_.description),
sqSent.getSelection()
)
);
em.createQuery(cq).getResultList();