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 — dev
– dev, Commented Mar 28, 2016 at 23:58

Lloyd Banks · Accepted Answer · 2014-08-05 15:52:54Z

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 5, 2014 at 15:52

Lloyd Banks

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3 Comments

Robert Moskal Over a year ago

That would be the other usual way. I like passing them in so I can easily mock them for testing.

Manatax Over a year ago

@RobertMoskal 's answer (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.

Honinbo Shusaku Over a year ago

@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?

Robert Moskal · Accepted Answer · 2022-06-14 18:15:07Z

11

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.

edited Jun 14, 2022 at 18:15

answered Aug 4, 2014 at 19:05

Robert Moskal

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2 Comments

Lloyd Banks Over a year ago

How is the object being passed here?

Robert Moskal Over a year ago

As long as you wrap each module in a function, it's just a repetition of the same pattern.

maryum375 · Accepted Answer · 2015-11-21 18:31:31Z

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.

Elad Nava · Accepted Answer · 2017-02-12 20:37:29Z

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, 2017 at 20:37

answered Sep 19, 2014 at 20:24

Elad Nava

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