/**
  * 判断用户名称是否重复
  */
 public function unique($attribute)
 {
     if (User::hasItem($attribute, $this->{$attribute}, $this->id) !== false) {
         $message = Yii::t('admin', '"{value}" 已经存在.');
         $params = ['attribute' => $this->getAttributeLabel($attribute), 'value' => $this->{$attribute}];
         $this->addError($attribute, Yii::$app->getI18n()->format($message, $params, Yii::$app->language));
     }
 }