PHP-DI

Introducing the PHP-DI bridge for Slim

Posted by Matthieu Napoli on March 8, 2016

Slim 3 was released 3 months ago and it was significant. It is one of the first frameworks to integrate the latest standards and concepts in its core:

  • PSR-7, a standard for HTTP messages like requests and responses
  • PSR-7 based middlewares, allowing framework-agnostic HTTP layers or even applications
  • container-interop, a standard for decoupling frameworks from dependency injection containers

While PSR-7 and middlewares are very interesting, what's more useful for us is the use of container-interop. That means Slim 3 can work with any dependency injection container.

It is very easy to replace the default container (Pimple) with PHP-DI, but today we are releasing a "PHP-DI - Slim" bridge that goes a little further. Read below for an introduction of what's possible with the PHP-DI bridge.

You can also read the full documentation for PHP-DI in Slim.

Controllers as services

While your controllers can be simple closures, you can also write them as classes and have PHP-DI instantiate them only when they are called:

class UserController
{
    private $userRepository;

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

    public function delete($request, $response)
    {
        $this->userRepository->remove($request->getAttribute('id'));

        $response->getBody()->write('User deleted');
        return $response;
    }
}

$app->delete('/user/{id}', ['UserController', 'delete']);

Dependencies can then be injected in your controller using autowiring, PHP-DI config files or even annotations.

Controller parameters

By default, Slim controllers have a strict signature: $request, $response, $args. The PHP-DI bridge offers a more flexible and developer friendly alternative.

Controller parameters can be any of these things:

  • request or response injection (parameters must be named $request or $response)
  • request attribute injection
  • service injection (by type-hint)

You can mix all these types of parameters together too. They will be matched by priority in the order of the list above.

Request or response injection

You can inject the request or response in the controller parameters by name:

$app->get('/', function (ResponseInterface $response, ServerRequestInterface $request) {
    // ...
});

As you can see, the order of the parameters doesn't matter. That allows to skip injecting the $request if it's not needed for example.

Request attribute injection

$app->get('/hello/{name}', function ($name, ResponseInterface $response) {
    $response->getBody()->write('Hello ' . $name);
    return $response;
});

As you can see above, the route's URL contains a name placeholder. By simply adding a parameter with the same name to the controller, PHP-DI will directly inject it.

Service injection

To inject services into your controllers, you can write them as classes. But if you want to write a micro-application using closures, you don't have to give up dependency injection either.

You can inject services by type-hinting them:

$app->get('/', function (ResponseInterface $response, Twig $twig) {
    return $twig->render($response, 'home.twig');
});

Note: you can only inject services that you can type-hint and that PHP-DI can provide. Type-hint injection is simple, it simply injects the result of $container->get(/* the type-hinted class */).

Installation

composer require php-di/slim-bridge

Usage

Instead of using Slim\App, simply use DI\Bridge\Slim\App:

<?php
require 'vendor/autoload.php';

$app = new \DI\Bridge\Slim\App;

You can then use the application just like a classic Slim application:

use Psr\Http\Message\ServerRequestInterface as Request;
use Psr\Http\Message\ResponseInterface as Response;

$app->get('/hello/{name}', function (Request $request, Response $response) {
    $response->getBody()->write('Hello!');
    return $response;
});

$app->run();

Learn more

You can read the full documentation for PHP-DI in Slim.

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