php laravel 判断是否存在

Question

 public function postCollect(Request $request)    {            $question= new Question;            $question_list->uesr_id = Auth::id();            $question_list->question_id = Input::get('question_id')            $question_list->question_answer = Input::get('question_answer');            $question_list->save();              return "success";        }