public function store()
 {
     $topic = new Topic();
     $validator = Validator::make(Request::except('_token'), Topic::$validatorTopic);
     if ($validator->fails()) {
         flash()->error("操作失败");
         return redirect()->back();
     }
     $topic->subject = Request::input('subject');
     $topic->body = clean(Request::input('body'));
     $topic->user_id = Auth::user()->user_id;
     $topic->node_id = Request::input('node_id');
     $topic->is_show = '1';
     $topic->save();
     flash()->success("发布成功");
     return redirect('/');
 }