Node MySQL - reusable connection module

Question

Question Updated:

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The solution should detail a simplified, proper model of a Node connection module allowing for the re-use of the connection by any module of a Node application needing to connect to a database. That way, the question might be useful for anyone with connection module issues in Node.

The answer might even include a way to pass in different credentials in order to connect to different tables or databases with a single function call from anywhere in an app.

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I wrote a script that utilized a number of simple modules to allow a user to post login data, have that data validated on the server, and if correct, receive a response of success. A very basic login functionality.

The problem: One user can log-in, but any more log-in attempts before I restart the server fail to connect to the database.

It appears that, because I'm declaring the connection in a variable in my module db_connect and requiring that module, the connection can't be re-used. It's being declared in the required module, and I had mistakenly believed that calling the variable in each connection attempt would recreate the connection. It doesn't.

The solution: As suggested by barry in the comments, in the db_connect module, I need to make the connection functionality a function rather than a variable, so I can then create the connection from within my validation script.

How can I do this? I'm trying to output the connection object when calling the createConnection() function, which is an exported method of db_connect.

db_connect:

console.log('db_connect module initialized');
var mysql      = require('mysql');

function createConnection(){
    var connection = mysql.createConnection({
        host     : 'localhost',
        user     : 'root',
        password : '',
        database : 'officeball'
    });
}

exports.createConnection = createConnection();
exports.mysql = mysql;

validator:

console.log('validator module initialized');
var connect = require("./db_connect");

function validate(username, password, callback){

    var createConnection = connect.createConnection();
    //the idea is for this to return the object, connection, 
    //which opens a new connection

    connection.connect(function (err){
        if (err) return callback(new Error('Failed to connect'), null);
        console.log('Connection with the Officeball MySQL database openned...');

        connection.query('select username,password,fname,lname,rank,active from users where username=?',
                username,
                function(err,rows,fields) {
                    connection.destroy();
                    console.log('...Connection with the Officeball MySQL database closed.');
                    if (err)
                        return callback(new Error ('Error while performing query'), null);
                    if (rows.length !== 1)
                        return callback(new Error ('- [Anomaly] - Failed to find exactly one user'), null);

                    if (rows[0].password === password & rows[0].active === "yes") {

                        var result = new Object;

                        result.username = rows[0].username;
                        result.password = rows[0].password;
                        result.fname = rows[0].fname;
                        result.lname = rows[0].lname;
                        result.rank = rows[0].rank;

                        return callback(null, result);

                    } if(rows[0].active !== "yes"){

                        return callback(new Error ('User account not active.'), null);

                    }else {

                        return callback(new Error ('Login credentials did not match.'), null);

                    }

                });


    });
};

exports.validate = validate;

Console log (originally, there was a connection error, but after my fix-attempt, the error is about the method):

C:\xampp\htdocs\officeball\node_scripts>node index.js
application initialized
server module initialized
login module initialized
validator module initialized
db_connect module initialized
sale module initialized
Server running at http://127.0.0.1:8080/
User username1 is attempting login...
TypeError: Property 'createConnection' of object #<Object> is not a function
    at Object.validate (C:\xampp\htdocs\officeball\node_scripts\custom_modules\v
alidator.js:6:33)
    at C:\xampp\htdocs\officeball\node_scripts\custom_modules\login.js:61:13
    at callbacks (C:\xampp\htdocs\officeball\node_scripts\node_modules\express\l
ib\router\index.js:164:37)
    at param (C:\xampp\htdocs\officeball\node_scripts\node_modules\express\lib\r
outer\index.js:138:11)
    at pass (C:\xampp\htdocs\officeball\node_scripts\node_modules\express\lib\ro
uter\index.js:145:5)
    at Router._dispatch (C:\xampp\htdocs\officeball\node_scripts\node_modules\ex
press\lib\router\index.js:173:5)
    at Object.router (C:\xampp\htdocs\officeball\node_scripts\node_modules\expre
ss\lib\router\index.js:33:10)
    at next (C:\xampp\htdocs\officeball\node_scripts\node_modules\express\node_m
odules\connect\lib\proto.js:193:15)
    at multipart (C:\xampp\htdocs\officeball\node_scripts\node_modules\express\n
ode_modules\connect\lib\middleware\multipart.js:93:27)
    at C:\xampp\htdocs\officeball\node_scripts\node_modules\express\node_modules
\connect\lib\middleware\bodyParser.js:64:9

Answer 1

Your problem was primarily what I mentioned in my comment, so I will make it an answer. Don't hurt yourself slapping your forehead. :-) See my inline comments below. You had one method invocation too many, an unreturned result, and a misnamed variable - otherwise, it works just fine.

db_connect.js

console.log('db_connect module initialized');
var mysql      = require('mysql');

function createConnection(){
    var connection = mysql.createConnection({
        host     : 'localhost',
        user     : 'root',
        password : '',
        database : 'officeball'
    });
    // ************ NOTE BELOW FOR CHANGE **************
    // You didn't return anything from this function. You need to return the connection
    return connection;
}
// ************ NOTE BELOW FOR CHANGE **************
// You are exporting a single connection by invoking createConnection();
// exports.createConnection = createConnection();
// what you want is:
exports.createConnection = createConnection;
exports.mysql = mysql;

validator.js

function validate(username, password, callback){
    // ************ NOTE BELOW FOR CHANGE **************
    // You had:
    // var createConnection = connect.createConnection();
    // but based on your code, you wanted to write this instead:
    var connection = connect.createConnection();

    /// ... REMAINDER OMITTED, because it was A-OK and this is already a long page
};

If you make those two three changes, you should be good to go. As ever, feel free to ask for any clarifications if it would be helpful.

Update This is how I am calling it - as you can see, I had it try to do it ever 2 seconds.

jt-test.js

var v = require('./validator');
var timers = require('timers');
var connections = 0;

timers.setInterval(function(){
    v.validate('bagehot','foo',function(err,result){
        if (err)
            console.log('failed', err);
        else
            console.log('success! ',result);
    });
},2000);

result

Connection with the Officeball MySQL database openned...
...Connection with the Officeball MySQL database closed.
success!  { username: 'bagehot',
  password: 'foo',
  fname: 'walter',
  lname: 'bagehot',
  rank: 12 }
Connection with the Officeball MySQL database openned...
...Connection with the Officeball MySQL database closed.
success!  { username: 'bagehot',
  password: 'foo',
  fname: 'walter',
  lname: 'bagehot',
  rank: 12 }
Connection with the Officeball MySQL database openned...
...Connection with the Officeball MySQL database closed.
success!  { username: 'bagehot',
  password: 'foo',
  fname: 'walter',
  lname: 'bagehot',
  rank: 12 }
Connection with the Officeball MySQL database openned...
...Connection with the Officeball MySQL database closed.
success!  { username: 'bagehot',
  password: 'foo',
  fname: 'walter',
  lname: 'bagehot',
  rank: 12 }

And so on. It runs indefinitely. Complete code for the three files is in this gist

Answer 2

You can checkout my emysql package.

https://www.npmjs.org/package/emysql

https://github.com/yanke-guo/enhanced-mysql-pool

Maybe it's some kind of outdated with the most recent node-mysql package, but still functional.