public function findByUnique($criteria)
    {
        if (!isset($criteria['slug'])) {
            return null;
        }

        return $this->_em->createQueryBuilder()
            ->select('p')
            ->from('VeonikBlogBundle:AbstractPost', 'p')
            ->where('p.slug = :slug')
            ->setParameter('slug', $criteria['slug'])
            ->getQuery()
            ->getResult();
    }