yii?制約の削除

数据表category: category_id category_titlesubcategory:subcategory_id subcategory_category(与category_id关联)      在删除category表的数据时,要确保category_id在subcategory_category中不存在控制器: public function actionDelete($id)    {        if(Yii::app()->request->isPostRequest)        {            $model=$this->loadModel($id);            $results = Category::getSubCategorySet($id);             //查找当前category_id是否在subcategory_category中存在                        //存在的话,就要提醒用户            //我这里是通过抛异常来提醒用户的,但我不想要错误编号的出现            //或者你们有更好的方法可以告诉我            if($results!=0){                throw new CHttpException(400,'This title is use on sub-category management');            }else{                $model = $this->loadModel($id);                $model->category_status = 'D';                if ($model->validate()) {                    $model->save();                }                // $model->delete();                // if AJAX request (triggered by deletion via admin grid view), we should not redirect the browser                if(!isset($_GET['ajax']))                    $this->redirect(isset($_POST['returnUrl']) ? $_POST['returnUrl'] : array('admin'));            }        }