问通过lodash和save()删除模型数据，不能在mongodb中持久化模型

EN

router.post('/accept-trades', function (req, res, next) {
  const {senderName, receiverName, senderId} = req.body;
  const user = req.user;
  console.log(senderName, receiverName);
  if (senderName) {
    User.findOne({ name: senderName })
    .then(sender => {
      _.remove(user.receivedTradeRequest, {username: senderName});
      _.remove(sender.sentTradeRequest, {username: receiverName});

      console.log('user.receivedTradeRequest', user.receivedTradeRequest);
      console.log('\n\nuser.sentTradeRequest', user.sentTradeRequest);

      async.parallel([
        function (cb) {
          user.save()
          .then(isSave => {
            cb(null, true);
          })
          .catch(err => {
            cb(err, null);
          });
        },
        function (cb) {
          sender.save()
          .then(isSave => {
            cb(null, true);
          })
          .catch(err => {
            cb(err, null);
          });
        }
      ], (err, results) => {
          if (err) {
            return res.status(500).json({
              message: 'Error: Trade is invalid as Card is already traded!',
            });
          }
          res.send('done');
          //res.redirect('/trade');
      });
    })
    .catch(err => {
      throw err;
    });
  } else {
    return res.status(500).json({
      message: 'Only accessible to logged in users!',
    });
  }
});