How do I use the same MySQL connection(s) for my entire Node.js app?

Question

I have an app.js. I run my entire app from there.

Inside app.js, I require many files that have code in it.

For each of these files, I do this:

var mysql = require('mysql');
var mclient = mysql.createConnection({
    host: settings.MYSQL.HOST,
    user: settings.MYSQL.USER,
    password: settings.MYSQL.PASSWORD,
    database: settings.MYSQL.DB,
});

Essentially, I am initiating a new connection for every file.

I want my app.js to make ONE connection, and then pass it to every file during the require line. How can I pass the connection to them so those files can use it?

(Or how can I pass a pool of connections to them?)

Answer 1

You can create a separate module, call it mysqlLib.js that will be responsible for creating a pool and returning connections:

var mysql = require("mysql");
var pool = mysql.createPool(/* credentials go here */);

exports.getConnection = function(callback) {
  pool.getConnection(function(err, conn) {
    if(err) {
      return callback(err);
    }
    callback(err, conn);
  });
};

and in any module/file that needs a mysql connection, you can do this:

var mysqlLib = require("mysqlLib");

mysqlLib.getConnection(function(err, mclient) {
  //do queries that you need
});

The way require() works, the code in mysqlLib.js will only be run once so only one pool will be created even if require("mysqlLib.js"} is called in multiple files. See this section of the node.js docs for an explanation of module cacheing.