Nodejs MySQL connection timeout

Question

When I run the application, It shows me Database is connected!

db.js

var mysql = require('mysql');
var settings = require('./config');
var db;
var exports = {};

exports.connectdb = function () {

 db = mysql.createConnection(settings.Database);

 db.connect(function(err){

     console.log('connecting');
     if(!err) {
         console.log('Database is connected!');
         return db;
     } else {
         console.log('Error connecting database!'+err);
         return null;
     }
 });

};

module.exports = exports;

but when i am trying to connect DB from user.js it shows me connection is null / TypeError: Cannot read property 'query' of undefined.

code block from user.js

var exports = {};
var dbcon = require('../config/db.js');
var dbconn = dbcon.connectdb();

exports.login = function(email,password) {

var userdetails = { name:email, password:password};

var dbconn = dbcon.connectdb();
if ( dbconn == null ) console.log('still nul');


dbconn.query("SELECT * FROM users where email = '"+email+"' and password = '"+password +"'", function (err, result) {
    if(err)
    {
        console.log(result[0]+' err');
        return null;
    }
});
};

module.exports = exports;

Answer 1

Node.js is asynchronous by nature. You are trying to use it in a synchronous fashion. To make this work, you must use the callback pattern. Below is an example:

db.js

var mysql = require('mysql');
var settings = require('./config');
var exports = {};

exports.connectdb = function (callback) {

 var db = mysql.createConnection(settings.Database);

 db.connect(function(err){
     callback(err,db);
 });

};

module.exports = exports;

user.js

var exports = {};
var dbcon = require('../config/db.js');

exports.login = function(email,password) {

    var userdetails = { name:email, password:password};

    dbcon.connectdb(function(err, dbconn){
        if ( err) //handle error


        dbconn.query("SELECT * FROM users where email = '"+email+"' and password = '"+password +"'", function (err, result) {
        if(err)
        {
           console.log(result[0]+' err');
        }
        });
    });
};

module.exports = exports;

From the code above you can see how the connectdb function accepts a function callback. When the database is connected the code will execute that callback to send the results. In the user.js file, you can now pass a callback function and use the results it gives you (the db). You can find more info about Node.js' asynchronous nature here. Basically, asynchronous code uses callbacks and synchronous code uses return statements. Returning values from asynchronous functions will most always yield null results as asynchronous callbacks will always fire "sometime" after the function is called.