Question

我想将计数器的值存储在MongoDB数据库中。在服务器创建时，我需要获得此计数器值。如果数据库为空，我创建一个文档并返回它，否则我获取文档。

问题是count方法是异步的。在发布快递时，myCounter的值仍为null。我应该如何修改此代码以创建myCounter？

import express from 'express'
import mongoose, { Schema } from 'mongoose'

mongoose.connect('mongodb://localhost/test')

var CounterSchema = new Schema({ value: Number })    
CounterSchema.methods.increment = function (cb) { this.value++; this.save() }    
var Counter = mongoose.model('Counter', CounterSchema)

var myCounter = null

Counter.count({}, (err, count) => {
  if (err) { return }
  if (!count) {
    myCounter = Counter({value: 0})
    return
  }
  if (count > 1) { return }
  Counter.findOne({}, {}, {}, (err, post) => {
    if (err) { return }
    myCounter = post
  })
})

console.log(myCounter) // Is still null :(

var app = express()    
app.get('/', (req, res) => {
  myCounter.increment() // Error if the request is quickly sent after the server start
  res.json(myCounter.value)
})    
app.listen(3000)

Answer 1

您可以尝试这样

import express from 'express'
import mongoose, { Schema } from 'mongoose'

mongoose.connect('mongodb://localhost/test')

var CounterSchema = new Schema({ value: Number })    
CounterSchema.methods.increment = function (cb) { this.value++ }    
var Counter = mongoose.model('Counter', CounterSchema)


console.log(myCounter) // Is still null :(

var myCounter = null

var app = express()

app.listen(3000,async () => {

  await Counter.count({}, (err, count) => {
    if (err) { return }
    if (!count) {
      myCounter = Counter({value: 0})
      return
    }
    if (count > 1) { return }
    Counter.findOne({}, {}, {}, (err, post) => {
      if (err) { return }
      instance = post
    })
  })
  app.get('/', (req, res) => {
      myCounter.increment()
      res.json(myCounter.value)
  })
})

这里我们在异步创建服务器之后立即分配myCounter变量，我们使用 await 关键字使代码同步工作。

如何与Mongoose同步获取文档？

1 个答案: