christinemoses / node-express-controller-lesson

Express with Controllers

Lesson Objectives

After this lesson, students should be able to...

• Explain the benefits of putting route handlers in controllers
• Separate their route handlers into controller modules
• Import controller modules into their routes file(s)
• Attach route handlers to their intended route and method

Terminology

Here's something you might see in an express routes file:

'use strict';

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

router.route('/').
    get(function(req, res) {
        res.json({});
    });

In this document, we will use the following terms regularly:

• router
• route
• route handler

For clarity, the following code segment will define these terms by assigning parts of the above code to variables with the above names:

'use strict';

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

var route = router.route('/');

var routeHandler = function(req, res) {
    res.json({});
};

route.get(routeHandler);

Why create controllers?

Creating controllers to store your route handlers is considered a best practice because it helps separate your concerns. If you are not using controllers, then your routes file includes both your routing logic and your controller logic.

The chief benefit of this practice, then, is that when there's a routing problem, you can look at just your routing logic. When a route handler is doing something wrong, you can look at just your handler.

How to create a controller

First, note that these are not your Rails-style controllers. What we're calling a controller here is just a storage bin for route handlers. This means that creating a controller can range from very easy to not that challenging, depending on what level of sophistication you demand.

Very basic controller object

First, let's look at the most basic controller you can create. Open up controllers/examplePOJOController.js in Sublime.

Notice how it's just an object literal with four methods.

Controller class

Now, let's look a slightly more sophisticated controller. Open up controllers/exampleController.js in Sublime.

Right off the bat, we can see it's an instance created by the Controller constructor function. It's clear that this file is only painting a partial picture.

Notice that the code in this file invokes a setter method on the Controller instance to register handlers for two HTTP methods. It then exports the instance so it can be required elsewhere.

Now, let's look at the constructor. Open up controllers/Controller.js in Sublime.

Squad discussion

Get into your squads and take 5 minutes to read and comprehend the contents of the file you just opened. After 5 minutes, I'll ask one or two squads to share their findings.

Connecting controllers and routes

Take a look at routes/index.js. Our first example of a controller is already connected with our root (/) route.

Squad discussion

Take 5 minutes with your squadmates to examine how the first example controller is connected to that route and how you can connect the second example controller to another route, /ex2. A squad may be chosen to present their code.

Demo

Link up the second controller example to the routes for the class to follow.