public function actionPay()
 {
     $modelDetail = new MerBase();
     //实例化商家信息
     $modelStu = new Students();
     //实例化学生
     $session = yii::$app->session;
     $mer_id = $session->get('mer_id');
     $user_info = $session->get('userinfo');
     $payDetail = $modelDetail->getSmall($mer_id);
     $user = $modelStu->getPassword($user_info['user_id']);
     return $this->render('payment', ['payDetail' => $payDetail, 'user' => $user]);
 }