Node.js 如何统计mongodb集合中特定字段的实例

这是我的mongodb中的收款

{
studentIDnumber: "111"
datepicker: "02/06/2019"
transactType: "Graduation expenses"
timepicker:"11:00am - 12:00pm"
amount:"123"
}

{
studentIDnumber: "111"
datepicker: "02/03/2019"
transactType: "Diploma"
timepicker:"11:00am - 12:00pm"
amount:"123"
}

{
studentIDnumber: "111"
datepicker: "02/03/2019"
transactType: "Tuition fee"
timepicker:"11:00am - 12:00pm"
amount:"123"
}

我试图计算集合中的11:00-12:00pm数量，但它给了我一个未处理的PromisejectionWarning:TypeError:无法读取未定义的属性“count”，下面是我的nodejs代码。正确的方法是什么？有什么想法吗

const mongoose = require('mongoose')
const url = require('../config/keys').MongoURI

router.get('/dashboard', ensureAuthenticated, (req, res) =>{
  res.render('dashboard', {
    firstname: req.user.firstname,
    lastname : req.user.lastname
  }),

  mongoose.connect(url, {useNewUrlParser: true}, function(err, db){
    if (err) throw err
    db.payments.count({timepicker: "11:00am - 12:00pm"})

  })

});

使用此查询：

db.payments.find({timepicker: "11:00am - 12:00pm"}).count(function(err, count) 
    {
        if (err) throw err;
        console.log(count);

    });

如果你使用猫鼬，那么

 PaymentModel.count({timepicker: "11:00am - 12:00pm"}, function(err, c) {
       console.log('Count is ' + c);
  });

---

您不需要每次都连接到数据库。一旦连接，mongoose构造器将其添加为全局。可能的重复工作！但我只是将计数替换为countDocuments，因为我收到一条警告，它将被弃用。