protected function addIndex($name, $cols)
    {
        if (empty($name)) {
            return Yii::t('podium/flash', 'Installation aborted! Index name missing.');
        }
        if (empty($cols)) {
            return Yii::t('podium/flash', 'Installation aborted! Index columns missing.');
        }
        try {
            $this->db->createCommand()->createIndex($this->getIndexName($name), $this->table, $cols)->execute();
            return $this->returnSuccess(Yii::t('podium/flash', 'Table index {name} has been added', [
                'name' => $this->getIndexName($name)
            ]));
        } catch (Exception $e) {
            return $this->returnError($e->getMessage(), __METHOD__,
                Yii::t('podium/flash', 'Error during table index {name} adding', [
                    'name' => $this->getIndexName($name)
                ])
            );
        }
    }