node.js design pattern for creating db connection once

mydb.js module:

var dbexports.db = function() {    if (db === null) {        db = dblibrary.createClient()    }    return db}

Other modules:

var db = require('mydb').db()...db.query(...)

This creates the DB client instance once at startup. I like this solution because the creation code is encapsulated in a separate module and the other modules can get access to the client with one require() statement.

Best answer I've seen for this is:

in start.js:

    function init_done() {      app.listen(8080);    }init_databases(init_done);

in databases.js:

init_databases(init_done_cb) {  db.create_async(/* connect data */ , function (err, res) {    if (err == null) init_done_cb();  });}

This way you can do the async startup of the database server without that awkward / dangerous waiting period.

I wrote connect-once just for solving this kind of problems. There are two main goals, that are achived by this module:

1. Connection should be initialized before request arrives
2. Connection should be initialized once, even there are multiple requests coming in at the same time

You can look at express-mongo-db and express-mongoose-db as examples of usage.