node, express and koa connect MongoDB in the same way. We use mongoose module to connect

Read this article about connecting to mysql: koa,express,node general method to connect MySQL

Here is just a brief list of the structure of connecting MongoDB. In fact, to really understand MongoDB, you need a lot of knowledge points, such as MongoDB data types and some API operations

Briefly speaking, MongoDB's structure

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Pay attention to my version

This is my catalog

Dependent version of my installation:

"dependencies": {
    "koa": "^2.6.2",
    "mongoose": "^5.3.12",
  }`

1. Connect MongoDB

// db/db.js
const mongoose = require('mongoose')

const DB_URL = 'mongodb://localhost:27017/local'

mongoose.connect(DB_URL)

mongoose.connection.on('connected',function() {
   console.log('Mongoose connection open to '+DB_URL);
});
/**
* Connection exception error database connection error
*/
mongoose.connection.on('error',function(err) {
  console.log('Mongoose connection error: '+ err);
});
/**
* disconnected the connection is abnormal
*/
mongoose.connection.on('disconnected',function() {
  console.log('Mongoose connection disconnected');
});

module.exports = mongoose

2. Set the set to be operated

// db/index.js
const mongoose = require('./db')
const Schema = mongoose.Schema;

const ceshiSchema = new Schema({
  title: String,
  body: String,
  date: Date
});

const MyModel = mongoose.model('ceshi', ceshiSchema);


class Mongodb {
  constructor () {

  }
// query
  query () {
     return new Promise((resolve, reject) => {
       MyModel.find({}, (err, res) => {
         if(err) {
           reject(err)
         }
         resolve(res)
       })
     })
  }
// Preservation
  save (obj) {
     const m = new MyModel(obj)
     return new Promise((resolve, reject)=> {
       m.save((err, res) => {
         if (err) {
           reject(err)
         }
         resolve(res)
         console.log(res)
       })
     })
     
  }
}
module.exports = new Mongodb()

Here is a simple example of query and save methods, or other methods. You can see the document specifically

3. Set up the server

// index.js
const Koa = require('koa')
const config = require('./config/default')
const ModelDb = require('./db')

const app =  new Koa()



app.use(async (ctx) => {
     let data = await ModelDb.query()
    ctx.body = data
    
})


app.listen(config.port)

console.log(`listening on port ${config.port}`)

4. Start the server

Open the browser, you can see the results of the query

Note: the premise is that there should be documents, that is, there should be data

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