public function findByCollectionNameIterator($collectionName)
    {
        /** @var QueryBuilder $queryBuilder */
        $queryBuilder = $this->entityManager->createQueryBuilder();
        return $queryBuilder
            ->select('PersistentResource')
            ->from($this->getEntityClassName(), 'PersistentResource')
            ->where('PersistentResource.collectionName = :collectionName')
            ->setParameter(':collectionName', $collectionName)
            ->getQuery()->iterate();
    }