Use async with NodeJs MySQL driver

Question

I want to reform the function router.get('/', etc) to one that uses async and await. The res.send and connection.query are making the trouble I don't know how to handle them using async/await constructs.

I tried to use this function:

const awaitHandlerFactory = (middleware) => {
    return async (req, res, next) => {
        try {
            await middleware(req, res, next)
        } catch (err) {
            next(err)
        }
    }
};

This is the code that i have in the file:

var express = require('express');
// const data = require("../data/repo");
var router = express.Router();

let mysql = require("mysql");
let config = require('../config/config.json');

let connection = mysql.createConnection(config);
connection.connect();
//
let guests = {};
let query1 = "select * from guests";
//GET home page.
 router.get('/', function(req, res, next) {
     connection.query(query1,  function (err, rows) {
         guests['guests'] = rows;
         res.send(guests)
     });
 });

this function works the router.get('/', etc...)

I get this: and this is what i want.

 "guests": [
        {
            "event_id": 1,
            "guest_id": 1,
            "firstName": "lkasjdl;skj",
            "lastName": "lskajdfal;skdj",
            "role": "lsakdjfalskdjflks;adjf",
            "created_at": null,
            "updated_at": null
        },

What do you get? We can not see the actual output. Where awaitHandlerFactory is used? — Ngob
– Ngob, Commented May 21, 2019 at 16:26

ChiralMichael · Accepted Answer · 2021-01-08 21:06:25Z

1

You need to convert the callback-style connection.query to something that can be awaited. promisify from util will do just that.

const express = require('express');
// const data = require("../data/repo");
const router = express.Router();

const util = require("util");
const mysql = require("mysql");
const config = require('../config/config.json');

const connection = mysql.createConnection(config);
const query = util.promisify(connection.query.bind(connection));
connection.connect();

const guests = {};
const query1 = "select * from guests";
//GET home page.
 router.get('/', async function(req, res, next) {
    try {
        const rows = await query(query1);
    } catch(ex) {
      //process your error
    }
    guests['guests'] = rows;
    res.send(guests);
 });

edited Jan 8, 2021 at 21:06

answered May 21, 2019 at 16:28

ChiralMichael

1,2249 silver badges20 bronze badges

Sign up to request clarification or add additional context in comments.

6 Comments

Ngob Over a year ago

This way its best to use promise implementation of mysql2

ChiralMichael Over a year ago

@ngob I'm not familiar with mysql2, but you're free to edit the answer.

iloq leo Over a year ago

@ChiralMichael Thank you for your answer. But i get this error when i try it on postman. -> node:22268) UnhandledPromiseRejectionWarning: TypeError: Cannot read property 'typeCast' of undefined -> Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 2) -> But if i use async and await i shouldnt use .catch() because it will do it for me. am i right?

ChiralMichael Over a year ago

@iloqleo No, you still need to catch exceptions (if you can process them). When using async/await you just try/catch like you would for synchronous code. I've edited my response to include this. You should process the error, if you can. In this case, there's not much for you to process. Usually, I'd just let the exception go and return the default 500 error. At any rate, take a look at your callstack to see where the error is coming from and fix that. I'm guess you aren't using connection.query correctly.

anondev Over a year ago

@iloqleo I have the same issue. I'm doing it exactly as ChiralMichael shows, so...

|

Collectives™ on Stack Overflow

Use async with NodeJs MySQL driver

1 Answer 1

6 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

6 Comments

Your Answer

Sign up or log in

Post as a guest

Related