Blog Archives

Auto injecting dependencies in PHP objects

I must admit I don’t really know what’s the correct title for this post. Finally I use “Auto injecting dependencies in PHP objects”. I know it isn’t very descriptive. Let me explain it a little bit. This time I want to automate the Hollywood Principle (“Don’t call us, we’ll call you”). The idea is simple. Imagine one “controller”

class Controller
{
    public function hi($name)
    {
        return "Hi $name";
    }
}

We can easily automate the “hi” action

$controller = new Controller();
echo $controller->hi("Gonzalo");

Or maybe if we are building a framework and our class name and action name depends on user-input:

$class = "Controller";
$action = "hi";
$arguments = ['name' => "Gonzalo"];

echo call_user_function_array([new $class, $action], arguments);

But imagine that we want to allow something like that:

class Controller
{
    public function hi($name, Request $request)
    {
        return "Hi $name " .$request->get('surname');
    }
}

Now we need to inject Request object within our action “hi”, but not always. Only when user set a input variable with the type “Request”. Imagine that we also want to allow this kind of injection in the constructor too. We can need to use Reflection to create our instance and to call our action. Sometimes I need to work with custom frameworks and legacy PHP applications. I’ve done it in a couple of projects, but now I want to create a library to automate this operation.

The idea is to use a Dependency Injection Container (Pimple in my example) and retrieve the dependency from container (if it’s available). I cannot use “new” keyword to create the instance and also I cannot call directly the action.

One usage example is:

class Foo
{
    public function hi($name)
    {
        return "Hi $name";
    }
}

class Another
{
    public function bye($name)
    {
        return "Bye $name";
    }
}

class Bar
{
    private $foo;

    public function __construct(Foo $foo, $surname = null)
    {
        $this->foo     = $foo;
        $this->surname = $surname;
    }

    public function hi(Another $another, $name)
    {
        return $this->foo->hi($name . " " . $this->surname) . ' ' . $another->bye($name);
    }
}

$container = new Pimple();
$container['name'] = "Gonzalo2";

$builder = new G\Builder($container);

$bar = $builder->create('Bar', ['surname' => 'Ayuso']);
var_dump($builder->call([$bar, 'hi']));

var_dump($bar->hi(new Another(), 'xxxxx'));

Our library tries to retrieve the dependecy from the DIC. If it cannot do it, it creates the a new instance.
The whole “magic” is in the Builder class. You can see the library in my github account.

Talk about Dependency Injection and Dependency Injection Containers at the deSymfony 2013 conference

The last week I attend to deSymfony conference. This year the conference was in Madrid and I collaborate as speaker with a talk about Dependency Injection and Dependency Injection Containers in PHP. It was a great experience. 400 attendees, two tracks, Fabien Potencier’s key-note and a brilliant organization could be one fast summary. We also could enjoy with good talks especially (in my humble opinion) one great talk about Advanced Silex with Javier Egiluz (please Javier write a book about Silex soon :) ). A good place to put the real face to colleagues and to know to the most important people at the PHP/Symfony community in Spain. Nice talks (and beers too) with people from Zaragoza, Extremadura, Valladolid, Valencia, Barcelona, with the people of Symfony-Madrid …

As I said before I participated as speaker with one talk about Dependencies, Containers and SOLID principles. Here you can see the slides of the talk.

The organization will publish soon the video with the talk (in Spanish). And here a couple of pictures of the talk.

desymfony2013.gonzalo123

2013-06-23 17.20.40

And that’s all. Thanks to the organization, the sponsors and of course to all the people who choose to attend to my talk one saturday at 9:30 AM. Say cheese …

desymfony2013.gonzalo123.people

Dependency Injection Containers with PHP. When Pimple is not enough.

Two months ago I wrote an article about Dependency Injection with PHP and Pimple. After the post I was speaking about it with a group of colleagues and someone threw a question:

What happens if your container grows up? Does Pimple scale well?

The answer is not so easy. Pimple is really simple and good for small projects, but it becomes a little mess when we need to scale. Normally when I face a problem like that I like to checkout the Symfony2 code. It usually implements a good solution. There’s something I really like from Symfony2: it’s a brilliant component library and we can use those components within our projects instead of using the full stack framework. So why don’t we only use the Dependency Injection component from SF2 instead Pimple to solve the problem? Let’s start:

We are going to use composer to load our dependencies so we start writing our composer.json file. We want to use yaml files so we need to add “symfony/yaml” and “symfony/config” in addition to “symfony/dependency-injection”:

{
    "require": {
        "symfony/dependency-injection": "dev-master",
        "symfony/yaml": "dev-master",
        "symfony/config": "dev-master"
    },
    "autoload":{
        "psr-0":{
            "":"lib/"
        }
    },
}

Now we can run “composer install” command and we already have our vendors and our autolader properly set.

We are going to build exactly the same example than in the previous post:

<?php
class App
{
    private $proxy;

    public function __construct(Proxy $proxy)
    {
        echo "App::__construct\n";
        $this->proxy = $proxy;
    }

    public function hello()
    {
        return $this->proxy->hello();
    }
}

class Proxy
{
    private $curl;

    public function __construct(Curl $curl)
    {
        $this->curl = $curl;
    }

    public function hello()
    {
        echo "Proxy::__construct\n";
        return $this->curl->doGet();
    }
}

class Curl
{
    public function doGet()
    {
        echo "Curl::doGet\n";
        return "Hello";
    }
}

Now we create our file “services.yml” describing our dependency injection container behaviour:

services:
  app:
    class:     App
    arguments: [@Proxy]
  proxy:
    class:     Proxy
    arguments: [@Curl]
  curl:
    class:     Curl

and finally we can build the script:

<?php
include __DIR__ . "/vendor/autoload.php";

use Symfony\Component\DependencyInjection\ContainerBuilder;
use Symfony\Component\DependencyInjection\Reference;
use Symfony\Component\Config\FileLocator;
use Symfony\Component\DependencyInjection\Loader\YamlFileLoader;

$container = new ContainerBuilder();
$loader = new YamlFileLoader($container, new FileLocator(__DIR__));
$loader->load('services.yml');

$container->get('app')->hello();

IMHO is as simple a Pimple but much more flexible, customizable and it’s also well documented. For example we can split our yaml files into different ones and load them:

<?php
include __DIR__ . "/vendor/autoload.php";

use Symfony\Component\DependencyInjection\ContainerBuilder;
use Symfony\Component\DependencyInjection\Reference;
use Symfony\Component\Config\FileLocator;
use Symfony\Component\DependencyInjection\Loader\YamlFileLoader;

$container = new ContainerBuilder();
$loader = new YamlFileLoader($container, new FileLocator(__DIR__));
$loader->load('services1.yml');
$loader->load('services2.yml');
$container->get('app')->hello();

An we also can use imports in our yaml files:

imports:
  - { resource: services2.yml }
services:
  app:
    class:     App
    arguments: [@Proxy]

If you don’t like yaml syntax and you prefer XML (I know. It looks insane :)) you can use it, or even programatically with PHP.

What do you think?

Source code in github (see the README to install the vendors)

Building a simple Dependency Injection Container with PHP

If you are looking for a small Dependency Injection Container with PHP maybe you need have look to Pimple.

Pimple is a small Dependency Injection Container for PHP 5.3 that consists of just one file and one class (about 50 lines of code).

Now, keeping with my aim of reinvent the wheel, we will create a simple Dependency Injection Container basically to understand how does it work. Let’s start.

First of all: Do we really need a Dependency Injection Container (DIC)? If you are asking yourself this question, maybe you need to have look to Fabien Poetencier’s article.

We are going to work with a teorical problem like this:

Imagine we are going to build a service that uses one external REST API. We define your application with three classes:

  • App. The main application.
  • Proxy The part of the application that speaks with the external API
  • Curl. One curl wrapper to perform our http connections to the REST API

Our first approach can be:

<?php
class App
{
    private $proxy;

    public function __construct()
    {
        echo "App::__construct\n";
        $this->proxy = new Proxy();
    }

    public function hello()
    {
        return $this->proxy->hello();
    }
}

class Proxy
{
    private $curl;

    public function __construct()
    {
        $this->curl = new Curl();
    }

    public function hello()
    {
        echo "Proxy::__construct\n";
        return $this->curl->doGet();
    }
}

class Curl
{
    public function doGet()
    {
        echo "Curl::doGet\n";
        return "Hello";
    }
}

$app = new App();
echo $app->hello();

If we execute the script:

php example1.php 

App::__construct
Proxy::__construct
Curl::doGet
Hello

It works but we have one problem. Our application is strongly coupled. As we can see App creates a new instance of Proxy within the constructor and Proxy creates a new instance of Curl. That’s a problem especially if we want to use TDD. What happens if we want to mock Curl requests to test the application without using the real external service?. Dependency injection can help us here. We can change our application to:

<?php
class App
{
    private $proxy;

    public function __construct(Proxy $proxy)
    {
        echo "App::__construct\n";
        $this->proxy = $proxy;
    }

    public function hello()
    {
        return $this->proxy->hello();
    }
}

class Proxy
{
    private $curl;

    public function __construct(Curl $curl)
    {
        $this->curl = $curl;
    }

    public function hello()
    {
        echo "Proxy::__construct\n";
        return $this->curl->doGet();
    }
}

class Curl
{
    public function doGet()
    {
        echo "Curl::doGet\n";
        return "Hello";
    }
}


$app = new App(new Proxy(new Curl()));
echo $app->hello();

The outcome is exactly the same but now we can easily use mocks and use different configurations depending on the environment. Maybe your testing development does not have access to the real REST server.

Now our application isn’t coupled but as we can see our Dependency Injection becomes a mess. That’s one problem with DI. It’s pretty straightforward to inject simple things but when we have dependencies over a set of classes that’s becomes a difficult task. Because of that we can use Dependency Injection Containers.

If we choose Pimple as Dependency Injection Container we can refactor our application to:

<?php
class App
{
    private $proxy;

    public function __construct(Pimple $container)
    {
        echo "App::__construct\n";
        $this->proxy = $container['Proxy'];
    }

    public function hello()
    {
        return $this->proxy->hello();
    }
}

class Proxy
{
    private $curl;

    public function __construct(Pimple $container)
    {
        $this->curl = $container['Curl'];
    }

    public function hello()
    {
        echo "Proxy::__construct\n";
        return $this->curl->doGet();
    }
}

class Curl
{
    public function doGet()
    {
        echo "Curl::doGet\n";
        return "Hello";
    }
}

require_once 'Pimple.php';

$container = new Pimple();
$container['Curl'] = function ($c) {return new Curl();};
$container['Proxy'] = function ($c) {return new Proxy($c);};

$app = new App($container);
echo $app->hello();

But what is my problem with Pimple? Basically my problem is that my IDE cannot autocomplete correctly $container is an instance of Pimple not the “real” instance. OK It instantiated on demand the classes but it’s done at runtime and the IDE don’t know about that. We can solve it using an extra PHPDoc to give hints to the IDE but we also can use a different approach. Instead of using Pimple we can use this script:

<?php
class App
{
    private $proxy;

    public function __construct(Container $container)
    {
        echo "App::__construct\n";
        $this->proxy = $container->getProxy();
    }

    public function hello()
    {
        echo "App::hello\n";
        return $this->proxy->hello();
    }
}

class Proxy
{
    private $curl;

    public function __construct(Container $container)
    {
        echo "Proxy::__construct\n";
        $this->curl = $container->getCurl();
    }

    public function hello()
    {
        return $this->curl->doGet();
    }
}

class Curl
{
    public function doGet()
    {
        echo "Curl::doGet\n";
        return "Hello";
    }
}

class Container
{
    public function getProxy()
    {
        return new Proxy($this);
    }

    public function getCurl()
    {
        return new Curl();
    }
}

$app = new App(new Container());
echo $app->hello();

The idea is the same than Pimple but now we have created our custom Dependency Injection Container without extending any library and now our IDE will autocomplete the fucntion names without problems. If we want to share objects instead creating new ones each time we call the factory function of the container we can change a little bit our Container (the same way than Pimple::share) with a simple singleton pattern:

class Container
{
    static $proxy;
    public function shareProxy()
    {
        if (NULL === self::$proxy) self::$proxy = new Proxy($this);
        return self::$proxy;
    }

    public function getCurl()
    {
        return new Curl();
    }
}

And that’s all. What do you think?

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