public function deliverQueryObject()
 {
     if (!isset($this->parent)) {
         $filesystem = new Filesystem();
         $this->parent = $filesystem->getRootFolder();
     }
     $this->query->andWhere('n.treeNodeParentID = :treeNodeParentID');
     $this->query->setParameter('treeNodeParentID', $this->parent->getTreeNodeID());
     return parent::deliverQueryObject();
 }