Laravel Controller Dependency Injection

Question

I'm trying to do dependency injection in Laravel to keep my controllers and models as slim as possible. The goal is to have repositories to handle the fetching of data attributed to certain models.

To this end I'm trying to follow the example from the documentation here and a popular Laravel boilerplate here

But I don't understand where the $user is coming from.

So looking at the boilerplate we have two files:

The ProfileController here

Excerpt below:

use App\Repositories\Frontend\Access\User\UserRepository;
/**
 * Class ProfileController.
 */
class ProfileController extends Controller
{
    /**
     * @var UserRepository
     */
    protected $user;
    /**
     * ProfileController constructor.
     *
     * @param UserRepository $user
     */
    public function __construct(UserRepository $user)
    {
        $this->user = $user;
    }

This looks a lot like the dependency injection mentioned in the docs, which is this:

class UserController extends Controller {

     /**
         * The user repository instance.
         */
        protected $users;

        /**
         * Create a new controller instance.
         *
         * @param  UserRepository  $users
         * @return void
         */
        public function __construct(UserRepository $users)
        {
            $this->users = $users;
        }

My problem is I don't understand where the $user is coming from.

In the UserRepository there is no $user defined as a parameter of the class itself. No where in the code is there any Auth::user() so I'm confused as to where the user instance is coming from.

$user is just the name of the variable. It could as well be $biggieSmalls or anything else. The variable just holds an instance of UserRepository. — DevK
– DevK, Commented Mar 15, 2017 at 18:20
@devk Where is that instance assigned to the variable? I understand it could be named anything, but I don't understand where it is assigned. It's not in the type-hinting is it? — Summer Developer
– Summer Developer, Commented Mar 15, 2017 at 18:21
Ah okay, sorry. Usually you bind them in service providers (let's say you wanted to bind implementation to interface, you would do it in service provider). But Laravel also has automatic resolution. Anyway, jfadich explained it better. — DevK
– DevK, Commented Mar 15, 2017 at 18:27

jfadich · Accepted Answer · 2017-03-15 18:22:36Z

18

In Laravel dependency injection is handled by the Container. I'm simplifying, but you can think of the container as a source of objects. If there is a singleton, its stored in the container. Otherwise the container knows how to instantiate objects for you. Whenever Laravel calls a method (like in a controller) or instantiates an object for you it will inspect the constructor and look for type hinted dependencies. If it sees a dependency it knows how to retrieve or create it will do so and pass it in for you.

So when Laravel instantiates the controller it looks at the constructor

public function __construct(UserRepository $user)
{
    $this->user = $user;
}

The container uses Type Hinting to see that it requires a UserRepository so it will instantiate a new one for you. It also does this recursively. So when it creates a new UserRepository it looks at that constructor and sees that it requires a RoleRepository so it will instantiate that as well.

TLDR: The service container inspects your dependencies and will instantiate them for you.

answered Mar 15, 2017 at 18:22

jfadich

6,3882 gold badges23 silver badges32 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

Summer Developer Over a year ago

Okay that makes sense. And then it looks like the Repository figures out which user it is based on the email that is being passed, don't understand why it doesn't just use Auth::user(); but I guess that is my next assignment! Thank you :)

xiarnousx Over a year ago

what about injecting classes that need to be configured using setters. Is there a factory pattern same as zend framework 2.4. thanks

jfadich Over a year ago

@xiarnousx I'm not familiar with Zend Framework so I'm not sure how it compares but you can define how an object should be constructed by binding it to the container Then Laravel will use that closure to build the object when you request it to be injected.

xiarnousx Over a year ago

@jfadich thanks, so basically we bind inside the AppServiceProviderService boot method. right? or create our own service provider and register it inside the kernel. I have not experiment it yet. thank you.

jfadich Over a year ago

@xiarnousx Either of those places would work. Which ever is appropriate would depend on the project. If it's a one off object then the AppServiceProvider would be just fine. If it's a larger project with lots of bindings it may be a good idea to create a custom service provider for each part of the app to keep the code clean and separated. Functionally it would be the same regardless of which service provider you do the binding in.

Community · Accepted Answer · 2017-05-23 12:25:17Z

Welcome to the dubious magic of Laravel. The basic idea with these dependency injections is that, depending on how you define your routes & controllers, Laravel can perform some automagical parsing of urls, identification of ids in those urls, and database fetching of objects.

My problem is I don't understand where the $user is coming from.

You should probably read the docs on the service container. You can also get a better idea of how your route definitions translate into parameter-laden urls with this command:

php artisan route:list

On one of my projects, this results in this output:

+--------+-----------+----------------------------+--------------------+-------------------------------------------------+--------------+
| Domain | Method    | URI                        | Name               | Action                                          | Middleware   |
+--------+-----------+----------------------------+--------------------+-------------------------------------------------+--------------+
|        | GET|HEAD  | /                          |                    | Closure                                         | web          |
|        | GET|HEAD  | api/user                   |                    | Closure                                         | api,auth:api |
|        | GET|HEAD  | categories                 | categories.index   | App\Http\Controllers\CategoryController@index   | web          |
|        | POST      | categories                 | categories.store   | App\Http\Controllers\CategoryController@store   | web          |
|        | GET|HEAD  | categories/create          | categories.create  | App\Http\Controllers\CategoryController@create  | web          |
|        | GET|HEAD  | categories/{category}      | categories.show    | App\Http\Controllers\CategoryController@show    | web          |
|        | PUT|PATCH | categories/{category}      | categories.update  | App\Http\Controllers\CategoryController@update  | web          |
|        | DELETE    | categories/{category}      | categories.destroy | App\Http\Controllers\CategoryController@destroy | web          |
|        | GET|HEAD  | categories/{category}/edit | categories.edit    | App\Http\Controllers\CategoryController@edit    | web          |
|        | GET|HEAD  | products                   | products.index     | App\Http\Controllers\ProductController@index    | web          |
|        | POST      | products                   | products.store     | App\Http\Controllers\ProductController@store    | web          |
|        | GET|HEAD  | products/create            | products.create    | App\Http\Controllers\ProductController@create   | web          |
|        | GET|HEAD  | products/{product}         | products.show      | App\Http\Controllers\ProductController@show     | web          |
|        | PUT|PATCH | products/{product}         | products.update    | App\Http\Controllers\ProductController@update   | web          |
|        | DELETE    | products/{product}         | products.destroy   | App\Http\Controllers\ProductController@destroy  | web          |
|        | GET|HEAD  | products/{product}/edit    | products.edit      | App\Http\Controllers\ProductController@edit     | web          |
+--------+-----------+----------------------------+--------------------+-------------------------------------------------+--------------+

And all those routes and their uris and parameters are generated from only a couple of very simple routes definitions. Here's my routes file:

$ cat routes/web.php
<?php

Route::get('/', function () {
    return view('master');
});

Route::resource('products', 'ProductController');
Route::resource('categories', 'CategoryController');

If you look at the list of URIs in the routes output above, you'll see parameters named in the URIs like {category} and {product}. These correspond to ids/keys in the URI which Laravel identifies. Laravel is "smart" enough to look at my Controller files, see the type-hinting in the various functions and detect that my function is expecting a depedency to be injected.

For instance, the Category controller's show method looks like this:

public function show(Tree $category)
{
    var_dump($category);
}

My controller might seem a little unusual because I'm type hinting that I want an object of type Tree, but Laravel is smart enough to recognize that I do in fact want a Model of type Tree, so it parses out the url and finds the id in it and automatically fetches the record in my db table trees with id matching the {category} fragment of my url and injects that into my function.

Note that I had some trouble when I tried to name the input parameter $tree instead of $category. That other thread may help answer your question a bit too.

The bottom line is that Laravel does a lot of "magic" to hopefully free you up from the tedious of manually defining your own code and queries to retrieve the objects you want.

Collectives™ on Stack Overflow

Laravel Controller Dependency Injection

2 Answers 2

5 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

5 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related