protected function addAlias($entity, $entity_id, $alias)
    {
        $this->alias->delete(array('entity' => $entity, 'entity_id' => $entity_id));

        $data = array(
            'alias' => $alias,
            'entity' => $entity,
            'entity_id' => $entity_id
        );

        return $this->alias->add($data);
    }