How to use the querybuilder in doctrine to test whether or not atleast one of two given values is already set in the dat

$qb->where($qb->expr()->andX(
    $qb->expr()->like('tags', '?1'),
    $qb->expr()->like('tags', '?2'),
    $qb->expr()->like('tags', '?3')
))->setParameters(array(
    1 => '%"a"%',
    2 => '%"b"%',
    3 => '%"c"%'
));

// don't forget the use statement for your repository up top
use Your\VswSystemCmsBundle\Repository\QuestionContentRepository;

// in buildForm() (this assumes you have $pageId set properly)
$builder
    ->add('questionContent', 'entity', array(
        'class'         => 'VswSystemCmsBundle:QuestionContent',
        'property'      => 'questionForForm',
        'query_builder' => function(QuestionContentRepository $repo) use ($pageId) { 
            return $repo->findNotAttachedQuestions($pageId);
        },
    ))
;

// this is Your\VswSystemCmsBundle\Repository\QuestionContentRepository class
public function findNotAttachedQuestions($pageId)
{
    $subQuery = $this->createQuery("
            SELECT  fq.questioncontent_id 
            FROM    VswSystemCmsBundle:FaqPageQuestionContent fq
            WHERE   fq.faqcontentpage_id = :page_id
        ")
        ->setParameter('page_id', $pageId)
    ;

    return $this->createQueryBuilder('q')
        ->where($qb->expr()->notIn('q.id', $subQuery))
    ;
}

// this is Your\VswSystemCmsBundle\Entity\QuestionContent class
public function getQuestionForForm()
{
    return substr($this->getQuestion(), 0, 30);
}