Call to undefined method Slice in Doctrine - symfony

Question

I have this function,
public function getWall(){
$q = $this->createQueryBuilder('f');
$q->leftJoin("f.profilo", 'p');
$q->leftJoin("p.utente", 'u');
$q->where('(f.foto_eliminata IS NULL OR f.foto_eliminata != 1)');
$q->andWhere('p.fase_registrazione = :fase');
$q->andWhere('u.locked = :false');
$q->slice(0, 20);
$q->setParameter(':fase', 100);
$q->setParameter('false', false);
$q->orderBy('f.created_at', 'desc');
$dql = $q->getQuery();
$results = $dql->execute();
return $results;
}
but I get this error,
Call to undefined method Doctrine\ORM\QueryBuilder::slice()

Answer 1

Ok, so, u get this error, cause QueryBuilder has no such method. But Collection has. If u want to use slice, a possible variant is:
use Doctrine\Common\Collections;
public function getWall(){
$result = $this->createQueryBuilder('f')
->leftJoin("f.profilo", 'p')
->leftJoin("p.utente", 'u')
->where('(f.foto_eliminata IS NULL OR f.foto_eliminata != 1)')
->andWhere('p.fase_registrazione = :fase')
->andWhere('u.locked = :false')
->setParameter('fase', 100)
->setParameter('false', false)
->orderBy('f.created_at', 'desc')
->getQuery()
->getResult();
// $result typed as array
return new Collections\ArrayCollection($result))->slice(0,20); // convert array to collection, then slice
}
By the way, it is not a good idea to 'limit' result of the query in a such way.
U can use setMaxResults(20), and not to select all objects at all.
About lazy collections (http://docs.doctrine-project.org/projects/doctrine-orm/en/latest/tutorials/extra-lazy-associations.html): after selecting result objects, u can take some object from result collection: $r = $result[0] after that:
$portfilos = $r->getPortfolio(); // returns for example Collection with some objects;
// its Lazy, without SQL query!
$portfolios->slice(0, 20); // queries first 20 potfolios
To use slice is a rather good idea, if u have lots of objects in some relation.
p.s. sry, mb I didn't recognized your problem, but tried :)
EDITED
fixed errors in code.