ExpressJS and passing variables between separate route files

Question

I'm using ExpressJs with Node.js and have put all my routes into a 'routes' folder.

On the server, I do my DB connection, then define my routes, like this:

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

var db;
dbconnect = new mongo.Db(config.mongo_database, new mongo.Server(config.mongo_host, config.mongo_port, {}), {});
dbconnect.open(function (err, db) {

  db.authenticate(config.mongo_user, config.mongo_pass, function (err, success) {
    if (success) {

      //routes/index.js
      app.get('/', routes.index);

      //routes/users.js
      app.get('/users', routes.users);

    }
  });
});

I want to access the 'db' object inside each of these routes javascript files. How would I pass that from this 'app.js' file to the index.js or users.js?

Thank you!

Answer 1

If you write your database abstraction in it's own file/module, you can then reuse it throughout your codebase as needed by just require()'ing it where needed. It won't get re-created if you write it correctly, and can just get initialized once on application startup like your example does.

//contents of your database.js file
var database;

module.exports = {

    init : function(config, cb) {
        database = new mongo.Db(config.mongo_database, new mongo.Server(config.mongo_host, config.mongo_port, {}), {});
        database.open(function (err, db) {  
            db.authenticate(config.mongo_user, config.mongo_pass, cb);
        });
    },

    query : function(params, cb) {
        database.query(params, cb);
    }   

};

This is a trivial example, but hopefully it gets the point across. In controllers or any files where you need that database object, you just...

var db = require('database');

db.init(params, function(err, db) {
    ...
});


db.query(params, function(err, db) {
    ...
});

The benefits are you now have a loosely coupled database object that can be used anywhere in your application just like any other node module through the require statement.

Answer 2

One suggestion is to expose your routes via a function which accepts a db parameter:

routes.js:

module.exports = function(db) {
    return {
        index: function(req, res, next) {
            // Funky db get stuff
        }
    }
}

Wrapping values in a closure like this and returning an object with more functions is a useful pattern, sometimes called "Revealing Module Pattern". It shows the dependencies clearly, allowing for easy testing (using e.g. a mock db object) while still using a flexible functional approach.