db.js

const env = process.env.NODE_ENV // 环境参数，是在 npm script 里设置的

let MYSQL_CONF
let REDIS_CONF

if (env === "dev") {
  // mysql
  MYSQL_CONF = {
    host: "localhost",
    user: "root",
    password: "123456",
    port: "3306",
    database: "my_blog2" // 相当于 use my_blog2
  }

  //redis
  REDIS_CONF = {
    port: 6379,
    host: "127.0.0.1"
  }
}

if (env === "production") {
  // mysql
  MYSQL_CONF = {
    host: "localhost",
    user: "root",
    password: "123456",
    port: "3306",
    database: "my_blog2" // 相当于 use my_blog2
  }

  //redis
  REDIS_CONF = {
    port: 6379,
    host: "127.0.0.1"
  }
}

module.exports = {
  MYSQL_CONF,
  REDIS_CONF
}

mysql.js

const mysql = require("mysql")
const { MYSQL_CONF } = require("../config/db")

// 创建链接对象
const con = mysql.createConnection(MYSQL_CONF)

// 开始连接
con.connect()

// 统一执行 sql 的函数
function exec(sql) { // sql 是 sql 语句
  const promise = new Promise((resolve, reject) => {
    con.query(sql, (err, result) => {
      if (err) {
        reject(err)
        return
      }
      resolve(result)
    })
  })
  return promise
}

module.exports = {
  exec,
  escape: mysql.escape
}

redis.js

const redis = require("redis")
const { REDIS_CONF } = require("../config/db")

// 创建客户端
const redisClient = redis.createClient(REDIS_CONF.port, REDIS_CONF.host)
redisClient.on("error", err => {
  console.error(err)
})

const set = (key, val) => {
  if (typeof val === "object") {
    val = JSON.stringify(val)
  }
  redisClient.set(key, val, redis.print) // redis.print 的作用是打印出是否 set 成功的消息
}

const get = key => {
  return new Promise((resolve, reject) => {
    redisClient.get(key, (err, val) => {
      if (err) {
        reject(err)
        return
      }
      if (val === null) { // 瞎传了一个 key，值可能是 null
        resolve(null)
        return
      }

      try { // 兼容 JSON 转换的这种格式，很巧妙！
        resolve(
          JSON.parse(val)
        )
      } catch (ex) {
        resolve(val)
      }
    })
  })
}

module.exports = {
  set,
  get
}