public function changeStatus(Request $request)
 {
     //user_id is autoincrement
     $data = $request->all();
     $info = ['user_id' => $data['user_id'], 'session_id' => $data['session_id'], 'status' => $data['status']];
     if (UserSessions::where('user_id', $info['user_id'])->where('session_id', $info['session_id'])->count() == 0) {
         $userSession = UserSessions::create($info);
         $changeCount = StudySession::where('id', '=', $info['session_id'])->increment('going_count');
     } else {
         if ($info['status'] == 1) {
             $changeCount = StudySession::where('id', '=', $info['session_id'])->increment('going_count');
         } else {
             $changeCount = StudySession::where('id', '=', $info['session_id'])->decrement('going_count');
         }
         UserSessions::where('user_id', $info['user_id'])->where('session_id', $info['session_id'])->update(['status' => $info['status']]);
     }
     $user = User::find($info['user_id']);
     return response()->json(['success' => 'true', 'cruz_id' => $user->cruz_id]);
 }