Two queries to fetch Category and sliced relationship

CategoryRepository2.php

<?php

namespace AppBundle\Repository;



use AppBundle\Entity\Category;
use Doctrine\Common\Collections\ArrayCollection;
use Doctrine\ORM\EntityRepository;
use Doctrine\ORM\Tools\Pagination\Paginator;

class CategoryRepository extends EntityRepository
{


    /**
     * Make several queries to load Category and slice of ManyToMany relationship
     * to Presentation entity whist paginating the relationship.
     *
     * WARNING: In this implementation Category is "owned" (weak) side of the
     * relationship. Thus if you try to flush the EntityManager, after calling
     * this method, it will NOT follow Category->Presentation ManyToMany relationship
     * and will NOT repersist it. However if in your implementation you will be
     * returning "owning" side of the relationship - you may want to unregister
     * this relationship with the EntityManager so that it can't be flushed anymore.
     *
     */
    function getCategoryByIdWithGivenAmountOfPresentations($id, $limit = 5, $offset){
        $em  = $this->getEntityManager();

        try {
            $dql_category = 'SELECT cat FROM AppBundle:Category cat WHERE cat.id = :id';

            $category = $em->createQuery($dql_category)             /** @var Category $category */
                ->setParameter('id', $id)
                ->getSingleResult();
        }
        catch(NoResultException $nrex){
            return null;
        }

        // also Presentation is owning side of the relationship, so it may be the case that
        // this join wouldn't work the other way around

        $presentations_array = $em
            ->createQuery('SELECT p,cat FROM AppBundle:Presentation p LEFT JOIN p.categories cat WHERE cat.id = :category_id')
            ->setFirstResult($offset)
            ->setMaxResults($limit)
            ->setParameter('category_id', $id)
            ->getResult();


        // we need to wrap in order for JMSSerializer to be able to traverse relationship
        $array_collection = new ArrayCollection($presentations_array);
        $category->setPresentations($array_collection);

        // the problem here is that if anyone tries to flush this
        // relationship, they may actually reset it...

        return $category;
    }


}