public function addObject($alias, $parent_id = null) {
        $query = array(
            'alias' => $alias,
            'parent_id' => $parent_id
        );

        $result = $this->find('first', array(
            'conditions' => $query
        ));

        if ($result) {
            return $result;
        }

        $this->create();

        if ($this->save($query)) {
            $this->deleteCache(array('RequestObject::hasAlias', $alias));

            return $this->getByAlias($alias);
        }

        return null;
    }