protected function countDrops()
    {
        $steps = array_reverse($this->steps);
        $drops = [];
        foreach ($steps as $step) {
            if (isset($step['call']) && $step['call'] === 'createTable') {
                $drops[] = $step;
            }
        }
        if (Yii::$app->session->get(self::SESSION_KEY, 0) === 0) {
            Yii::$app->session->set(self::SESSION_STEPS, count($drops));
        }
        return $drops;
    }