public function getAllRootIds()
    {
        $entityClass = $this->getEntityClass();

        $query  = $this->getObjectManager()->createQuery('SELECT DISTINCT c.root FROM ' . $entityClass . ' c');
        $result = $query->getResult();

        $rootIds = array();
        foreach ($result as $resultArray) {
            $rootIds[] = $resultArray['root'];
        }

        return $rootIds;
    }