Cannot read property 'query' of undefined - MySQL NodeJS

Question

I got this type of error when I try to make a post request to my node js server. I link here the error and the two files so you can understand better what I have done.

TypeError: Cannot read property 'query' of undefined
    at checkIfUserCodeExist (/usr/my_server/addReferFriend.js:13:29)
    [...]

I got two files: app.js and addReferFriend.js

app.js:

var express = require('express');
var path = require('path');
var logger = require('morgan');
var cookieParser = require('cookie-parser');
var bodyParser = require('body-parser');
var mysql= require('mysql2');
var http = require('http');
var app = express();

var addReferFriend = require('./addReferFriend');

app.set('views', path.join(__dirname, 'views'));
app.set('view engine', 'ejs');

app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: false }));
app.use(cookieParser());
app.use(express.static(path.join(__dirname, 'public')));


app.use(async function(req, res, next) {
  try {
    if( req.dbConnection ) {
      // ensure that req.dbConnection was not set already by another middleware
      throw new Error('req.dbConnection was already set')
    }

    let connection = mysql.createConnection({
            host: 'xx',
        user: 'xx',
        password: 'xx',
        database: 'xx'
    });

    res.on("finish", function() {
      // end the connection after the resonponse was send
      req.dbConnection.end()
    });

    // wait for the connection and assign it to the request
    req.dbConnection = await connection.connect();
    next();
  } catch(err) {
    next(err);
  }
});

app.use('/api/addReferFriend', addReferFriend);

// catch 404 and forward to error handler
app.use(function(req, res, next) {
  var err = new Error('Not Found');
  err.status = 404;
  next(err);
});

module.exports = app;
var server = http.createServer(app);
server.listen(3955);

and addReferFriend.js:

var express = require('express');
var router = express.Router();

/* GET users listing. */
router.post('/', function(req, res, next) {
  var uid = req.body.uid;
  var friendReferCode = req.body.friendReferCode;

  var sqlCheckIfExist = "SELECT my_refer FROM hub_user WHERE my_refer = '" + friendReferCode + "'";
  var sqlCodeCheckSameAsMine = "SELECT my_refer FROM hub_user WHERE uid = '" + uid + "'";

  function checkIfUserCodeExist() {
    return req.dbConnection.query(sqlCheckIfExist)
      .then(([rows, fields]) => {
        if (rows == 0) {
          console.log("Non esiste!")

          return res.send(JSON.stringify({
            "status": 500,
            "response": "codeNotExist"
          }));
        }
        console.log("Esiste!")
        console.log(rows[0].my_refer);
        return checkIfCodeIsSameAsMine(connection)
      })
  }

  function checkIfCodeIsSameAsMine() {
    return req.dbConnection.query(sqlCodeCheckSameAsMine)
      .then(([rows, fields]) => {
        if (rows == friendReferCode) {
          console.log("Codice uguale!")
          return res.send(JSON.stringify({
            "status": 500,
            "response": "sameCodeAsMine"
          }));
        }
        console.log("Codice non uguale!")
      })
  }

  checkIfUserCodeExist()
   .catch(next)
});
module.exports = router;

I am using Mysql2. Can somebody help me to fix the error?

Thanks in advance, Michele.

The app.use('/api/addReferFriend', addReferFriend); has to be after the app.use(async function(req, res, next) { .. let connection = mysql.createConnection( ... }) in the main.js because middlewares are executed the order they are registered. — t.niese
– t.niese, Commented Dec 27, 2018 at 16:58

A.Mlaouhi · Accepted Answer · 2018-12-28 00:02:02Z

1

use this package: - const mysql = require('mysql2/promise');

`app.use(async function (req, res, next) {
if (req.dbConnection) {
    next();
}
mysql.createConnection({
    host: 'xx',
    user: 'xx',
    password: 'xx',
    database: 'xx'
}).then((conn) => {
    req.dbConnection = conn;
    next();
}).catch((error) => {
    next(error);
});

});`

and replace this code:

 module.exports = app;
 var server = http.createServer(app);
 server.listen(3955);

by this :

app.listen(3955, () => {
    console.log("Server listening on port : " + 3955);
});
module.exports = app;

You must control addReferFriend.js and remove a catch in end of script

answered Dec 28, 2018 at 0:02

A.Mlaouhi

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t.niese · Accepted Answer · 2018-12-27 17:14:34Z

1

The app.use('/api/addReferFriend', addReferFriend); has to be after the app.use(async function(req, res, next) { .. let connection = mysql.createConnection( ... }) in the main.js because middlewares are executed the order they are registered.

answered Dec 27, 2018 at 17:14

community wiki

t.niese

1 Comment

Michele Zotti Over a year ago

Editing in this way I got: Cannot read property 'end' of undefined app.js:45:24 here precisely: req.dbConnection.end()

Walter Barbagallo · Accepted Answer · 2018-12-28 13:32:10Z

0

connection.connect() returns void (check the sources); so req.dbConnection is set to undefined.
You have to wait the connect event and then bind the connection to req and finally call next.

Otherwise, after a fast reading of mysql2 documentation, you can simplify with this middleware:

app.use(function(req, res, next) {
  if (req.dbConnection) {
    next();
  }
  else {
    req.dbConnection = mysql.createConnection({
      host: 'xx',
      user: 'xx',
      password: 'xx',
      database: 'xx'
    });
    next();
  }
})

In my opinion you have to create the connection once and not on every request.

edited Dec 28, 2018 at 13:32

answered Dec 27, 2018 at 22:31

Walter Barbagallo

2512 silver badges6 bronze badges

2 Comments

Michele Zotti Over a year ago

Look this: stackoverflow.com/questions/53951525/…

Michele Zotti Over a year ago

how can i do what you said?

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