public function saving($model)
 {
     $tag_model = new \App\Tag();
     // RULES
     if (is_array($model->tag_ids)) {
         foreach ($model->tag_ids as $k => $v) {
             $rules['tag_ids' . $k] = ['exists:' . $tag_model->getTable()];
         }
     } else {
         $rules['tag_ids'] = ['exists:' . $tag_model->getTable()];
     }
     $validator = Validator::make($model->toArray(), $rules);
     if ($validator->fails()) {
         $model->setErrors($validator->messages());
         return false;
     }
 }