NodeJS / Express - Make Available MySQL Connection Object in Router File

Question

I have the following in my app.js file:

var mysql = require('mysql');
var connection = mysql.createConnection({
    host: 'localhost',
    port: 3306,
    user: 'user',
    password: 'password',
    database: 'mydatabase'
});
connection.connect();

In routes/index.js, I currently have only the boilerplate code:

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

module.exports = router;

How do I make available the connection object from the app.js file in routes/index.js?

Possible duplicate of [How to properly pass mysql connection to routes with express.js](http://stackoverflow.com/questions/16800418/how-to-properly-pass-mysql-connection-to-routes-with-express-js) — dev, Mar 28 '16 at 23:58

score 15 · Accepted Answer · answered Aug 05 '14 at 15:52

15

I ended up splitting the database connection logic from the app.js file. In a separate file called connection.js, I have the following:

var mysql = require('mysql');

var connection = mysql.createConnection({
    host: 'localhost',
    port: 3306,
    user: 'user',
    password: 'password',
    database: 'mydatabase'
});

module.exports = connection;

Then in my route file, I add

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

to the top of the file where all my other modules are brought in. In my instance, the connection.js file is one level higher than my route file, hence the ../ in the require() function parameter.

answered Aug 05 '14 at 15:52

Lloyd Banks

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1

That would be the other usual way. I like passing them in so I can easily mock them for testing. – Robert Moskal Aug 06 '14 at 04:25
@RobertMoskal 's answer (http://stackoverflow.com/a/25125755/1489912) is better, because you can use it for connection pooling. This one will eventually leave you with no control over the connections created. – Manatax Sep 16 '15 at 03:57
@LloydBanks in this example, is a new DB connection being instantiated in every file that has `var connection = require('../connection');`? So, does that mean, if we separate our routes into different files, we should close the connection after the route handlers are done using the connection? – Honinbo Shusaku Sep 06 '16 at 12:05

Robert Moskal · Answer 2 · 2022-06-14T18:15:07.997

My preference is to do some simple dependency injection and pass the required resource into the router by wrapping the module in a function:

var express = require('express');

module.exports = function (connection) {
    var router = express.Router();
    //do stuff with the connection
    return router;

}

Then you just instantiate the router module in app.js as a function with the database connection as an argument:

app.use('/where/ever', require('./module-b')(connection));

Usually I wrap up the dependencies in an object:

app.use('/where/ever', require('./module-b')({db:connection}));

This way you don't have to keep changing the function signature as dependencies are added. This gives you a super-lightweight inversion of control container for your express applications.

As long as you wrap each module in a function, it's just a repetition of the same pattern. — Robert Moskal, Sep 05 '16 at 23:26

Elad Nava · Answer 3 · 2017-02-12T20:37:29.927

0

Check out express-myconnection, it lets you access the MySQL connection from within your routes.

Update: After using express-myconnection in production, I would not recommend it - it leaks connections, causing requests to hang (callback will never be called), and it is no longer actively maintained.

edited Feb 12 '17 at 20:37

answered Sep 19 '14 at 20:24

Elad Nava

7,746
2
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61

score 0 · Answer 4 · answered Nov 21 '15 at 18:31

I had the same problem, and Lloyds' suggestion was kind of a solution for me but I just didn't want to be stuck on a single type of db, I want to be able to move my app to another db with just a new implementation of a single class. So that worked for me:

function DataAccess(connectionData) {
    //Using the connectionData...
}

var _dataAccessInstance;

module.exports = function (connectionData) {
    if (!_dataAccessInstance) {
        _dataAccessInstance = new DataAccess(connectionData)
    }
    return _dataAccessInstance;
};

And then the usage will be just require the file:

//The object is the connection data to be sent to the module
var dataAccess = require('./data-access')({});

Sure, this has its own flaws like every module must know and send the connection data. But I assume the data is stored in the configuration and all hte modules can access it.

NodeJS / Express - Make Available MySQL Connection Object in Router File

4 Answers4