public function post($id, $content)
 {
     $validator = new Validation();
     $validator->setRule('required', $content);
     if (!$validator->validate()) {
         Session::setError($validator->getErrors());
         Redirect::back();
     }
     if ($this->comment->add(Auth::getUserId(), $id, $content) !== 1) {
         Session::setError('something went wrong');
         Redirect::back();
     }
     Session::setMessage('Done');
     Redirect::to('/product/' . $id);
 }