Nodejs(Express) - 08 数据库Mysql

一、mysql

1.1 安装

window系统下载msi版按照向导安装Mysql，下载地址：https://pc.qq.com/detail/3/detail_1303.html，包含了mysql server，workbench等。

安装后打开mysql commain line工具，输入root密码登录。可通过命令行操作数据库。

mysql command line.png

或打开MySql Workbench连接本地数据库进行数据库的管理

连接数据库

1.2 准备数据

CREATE TABLE table_name (column_name column_type); 创建表

CREATE TABLE `user` (
  `id` int NOT NULL AUTO_INCREMENT,
  `name` varchar(50) DEFAULT NULL,
  `age` tinyint DEFAULT NULL,
  PRIMARY KEY (`id`)
)ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;

INSERT INTO table_name ( field1, field2,...fieldN ) VALUES( value1, value2,...valueN ); 插入数据

INSERT INTO `user` (`id`, `name`, `age`)
VALUES
    (1,'Mark',40),
    (2,'Dell',33),
    (3,'Timo',28);

二、express连接mysql

2.0 初始化项目

express hello-express

初始项目目录

db目录为业务增加的数据库管理文件夹

2.1 安装mysql包

npm install mysql

2.2 准备mysql配置

db目录下创建command.js文件存放操作语句，代码如下：

const INSERT = 'INSERT INTO user (id, name, age) values (0, ?, ?)'
const SELECTALL = 'select * from my_users'
const SELECT = 'select * from my_users where id = ?'
const DELETE = 'delete from my_users where id = ?'
const UPDATE = 'update my_users set name=?, age=? where id=?'

module.exports = {
  INSERT,
  SELECTALL,
  SELECT,
  DELETE,
  UPDATE
}

2.3 查询数据库

db目录增加sql.js，增加查询代码

const CONFIG = {
  host: 'localhost',
  port: 3306,
  user: 'user',
  password: 'user123',
  database: 'mysql'
}
const mysql = require('mysql')
const pool = mysql.createPool(CONFIG)

const run = (command, params) => {
  return new Promise((resolve, reject) => {
    pool.getConnection((error, connection) => {
      if(error) reject('mysql connection error')
      
      console.log(command)
      connection.query(command, params, (err, result) => {
        err ? reject(err) : resolve(result)
      })
    })
  })
}

module.exports = {
  run
}

在routes/users.js增加路由响应

var express = require('express');
var router = express.Router();
var command = require('../db/command')
var mysql = require('../db/sql')

/* GET users listing. */
router.get('/', async (req, res, next) => {
 try {
   const result = await mysql.run(command.SELECTALL)
   res.send(result)
 } catch(err) {
   res.status(500).send(err)
 }
});

router.get('/:user_id', async (req, res, next) => {
 try {
   const id = req.params.user_id
   const result = await mysql.run(command.SELECT, id)
   res.send(result)
 } catch(err) {
   res.status(500).send(err)
 }
});


module.exports = router;

浏览器访问http://localhost:3000/users则得到users串

浏览器访问http://localhost:3000/users/1则得到id为1的用户信息

三、Troubleshooting

1. 连接数据库出错

错误信息： Error: ER_NOT_SUPPORTED_AUTH_MODE: Client does not support authentication protocol requested by server; consider upgrading MySQL client

错误原因：原因8.0mysql引入了caching_sha2_password模块作为默认身份验证插件，nodejs还没有跟进

解决方案：进入mysql命令行工具，执行下面命令
ALTER USER ‘userName’@'HostName' IDENTIFIED WITH mysql_native_password BY '自己的密码';
如： ALTER USER 'root'@'localhost' IDENTIFIED WITH mysql_native_password BY 'admin123';

2. response发送响应时报错

错误信息： Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
错误原因： send()发送后，next()又发送，重复发送请求。
解决方案：把next删除

image.png

或这种解决方案：https://www.cnblogs.com/codebook/p/10040501.html