Node.js 如何禁止添加mongodb中已经存在的具有相同objectId的较小数字？

如果我有这样的收藏：

_id: ObjectId("5ae4e704b7bccf133c24f0b8")
electoralUnit:ObjectId("5ab906612f30fe23dc592591")
turnoutByHour:"08:00"
voterTurnout:11
safeVoter:1
date:2018-04-28T21:26:28.678Z
__v:0

如何禁止下一次输入，即09:：00 in field turnoutByHour中的输入，不能是VoterTrump field小于11的数字，但仅当ElectorNunit是相同的id时

我用if语句想象了一些东西，比如：

if (req.body.voterTurnout < VoterTurnouts.findOne({voterTurnout : req.params.voterTurnout }))

---

所以我只需要添加这个…

这很简单？在xxx.findOne之后使用if statement？我不确定你的意思以及应该是什么样子？Oke xxx.findOne（{…}）.exec（函数（err，result）{if（req.body.voter..但是，如何将turnoutByHour和ElectorUnnit包括在if语句中？我添加route让您看到我有很多带有错误消息的if语句，但我不知道如何添加此语句。

router.post('/', (req, res)=>{
    let errors = [];

    if (!req.body.electoralUnit) {
      errors.push({message: 'Must chooose Electoral Unit!'});
    }
    if (!req.body.voterTurnout) {
      errors.push({message: 'Must add Voter Turnout!'});
    }

    if (errors.length > 0) {
      res.render('home/voterTurnouts/index', {
        errors: errors,
        electoralUnit: req.body.electoralUnit,
        voterTurnout: req.body.voterTurnout
      });
    } else {
      VoterTurnout.findOne({_id: req.params.id}).then(voterTurnout=>{
          const newVoterTurnout = VoterTurnout({
            electoralUnit: req.body.electoralUnit,
            turnoutByHour: req.body.turnoutByHour,
            voterTurnout: req.body.voterTurnout,
            safeVoter: req.body.safeVoter
          });
          newVoterTurnout.save().then(savedVoterTurnout=>{
            ElectoralUnit.find({}).then(electoralUnits=>{
              res.redirect('/voterTurnouts');
            });
          }).catch(errors=>{
            req.flash('error_message', 'Hours are already added with that Electoral Unit!');
            res.redirect('/voterTurnouts');
          });
      });
    }
});