## **Dependency Injection** ### **The Problem** The foundation of the Laravel framework is its powerful IoC container. To truly understand the framework, a strong grasp of the container is necessary. However, we shold note that an IoC container is simply a convenience mechanism for achieving a software design pattern: dependency injectionl. A container is not necessary to perform dependency injection, it simply makes the task easier. First, let's explore why dependency injection is beneficial. Consider the following class and method: ~~~ class UserController extends BaseController{ public function getIndex() { $users= User::all(); return View::make('users.index', compact('users')); } } ~~~ While this code is concise, we are unable to test it without hitting an actual database. In other words, the Eloquent ORM is tightly coupled to out controller. We have no way to use or test this controller without also using the entire Eloquent ORM, including hitting a live database. This code also violates a software design principle commonly called separation of concerns. Simple put: our controller knows too much. Controllers do not need to know where data comes from, but only how to access it. The controller doesn't need to know that the data is available in MySQL, but only that it is available somewhere. > **Separation Of Concerns** > > Every class should have a single responsibility, and that responsibility should be entirely encapsulated by the class. > So, it will be beneficial for us to decouple our web layer (controller) from our data access layer completely. This will allow us to migrate storage implementations easily, as well as make our code easier to test. Think of the "Web" as just a transport layer into your "real" application. Imagine that your application is like a monitor with a variety of cable ports. You can access the monitor's functionality via HDMI, VGA, or DVI. Think of the Internet as just a cable into your application. The bulk of a monitor's functionality is independent of the cable. The cable is just a transport mechanism just like HTTP is a transport mechanism for your application. So, we don't want to clutter up our transport mechanism (the controller) with application logic. This will allow any transport layer, such as an API or mobile application, to access our application logic. So, instead of coupling our controller to the Eloquent ORM, let's inject a repository class.