先做个总结：连接数据库是一个建库，建Schema的过程...之后就是利用实例化的对象进行数据库的操作...
1.moogoDB的连接
//database.jsvar mongoose = require('mongoose')mongoose.connect('mongodb://localhost:27017/lagou', { useNewUrlParser: true})var db = mongoose.connectiondb.on('error', console.error.bind(console, 'connection error:'))db.once('open', function () { // we're connected!})module.exports = mongoose //某一个model的代码const mongoose = require('../utils/database')// 创建Schema，创建集合const positionSchema = new mongoose.Schema({ companyLogo: String, companyName: String, positionName: String, city: String, salary: String, createDate: String})const PositionModel = mongoose.model('positions', positionSchema)//之后进行一些增删改查的操作 2.mysql的连接
//连接数据库var mysql = require('mysql');var connection = mysql.createPool({ connectionLimit : 10, host : 'localhost', user : 'root', password : '', database : 'gp7'}); //然后做增删改查的工作//查const _select = (sql) => { return new Promise((resolve, reject) => { connection.query('SELECT * FROM posts')//暂定查所有 .on('error', (err) => { reject(err.message) }) .on('result', (row) => { resolve(row) }) })}