Dependency Injection Zendcon 2010 101104172213 Phpapp01

8/2/2019 Dependency Injection Zendcon 2010 101104172213 Phpapp01

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Dependency Injection

Fabien Potencier


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Fabien Potencier

Serial entrepreneurDeveloper by passion

Founder of Sensio

Creator and lead developer of Symfony

On Twitter @fabpot

On github http://www.github.com/fabpotBlog http://fabien.potencier.org/


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A real world web example


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In most web applications, you need to manage the user preferences

The user language Whether the user is authenticated or not The user credentials


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This can be done with a User object

setLanguage(), getLanguage()setAuthenticated(), isAuthenticated()addCredential(), hasCredential()...


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The User informationneed to be persisted

between HTTP requests

We use the PHP session for the Storage


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class SessionStorage{

function __construct($cookieName = 'PHP_SESS_ID'){

session_name($cookieName);session_start();

}

function set($key, $value){

$_SESSION[$key] = $value;}

// ...}


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class User{

protected $storage;

function __construct(){

$this->storage = new SessionStorage();}

function setLanguage($language){

$this->storage->set('language', $language);}

// ...}

$user = new User();

Veryeasytouse

Veryhardto

customize


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class User{

protected $storage;

function __construct($storage){

$this->storage = $storage;}

}

$storage = new SessionStorage();

$user = new User($storage);Slightlymore

difficulttouse

Veryeasyto

customize


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Thats Dependency Injection

Nothing more


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Lets understand why the first example

is not a good idea


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I want to change the session cookie name


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class User{

protected $storage;


$this->storage = new SessionStorage('SESSION_ID');}

function setLanguage($language){$this->storage->set('language', $language);

}

// ...}

$user = new User();

Hardcodeitinthe

Userclass


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class User{

protected $storage;


$this->storage = new SessionStorage(STORAGE_SESSION_NAME);}

}

define('STORAGE_SESSION_NAME', 'SESSION_ID');

$user = new User();

Addaglobal

configuration?


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class User{

protected $storage;

function __construct($sessionName){

$this->storage = new SessionStorage($sessionName);}

}

$user = new User('SESSION_ID');

ConfigureviaUser?


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class User

{protected $storage;

function __construct($storageOptions){

$this->storage = new SessionStorage($storageOptions['session_name']);

$user = new User(array('session_name' => 'SESSION_ID')

); Configurewithanarray?


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I want to change the session storage implementation

Filesystem

MySQLMemcached


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class User{

protected $storage;


$this->storage = Registry::get('session_storage');

}}

$storage = new SessionStorage();Registry::set('session_storage', $storage);

$user = new User();

Useaglobal

registryobject?


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Now, the User depends on the Registry


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Instead of harcoding

the Storage dependency

inside the User class constructor

Inject the Storage dependency

in the User object


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class User



$this->storage = $storage;}}

$storage = new SessionStorage('SESSION_ID');$user = new User($storage);


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What are the advantages?


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Use different Storage strategies


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class User

{ protected $storage;



$storage = new MySQLSessionStorage('SESSION_ID');$user = new User($storage);

Useadifferent

Storageengine


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Configuration becomes natural


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class User

{ protected $storage;



$storage = new MySQLSessionStorage('SESSION_ID');$user = new User($storage);

Configuration

isnatural


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Wrap third-party classes (Interface / Adapter)


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class User{

protected $storage;

function __construct(SessionStorageInterface $storage){

$this->storage = $storage;}

}

interface SessionStorageInterface{

function get($key);

function set($key, $value);}

Addaninterface


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Mock the Storage object (for testing)

class User{


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function __construct(SessionStorageInterface $storage)

{$this->storage = $storage;

}}

class SessionStorageForTests implements SessionStorageInterface{

protected $data = array();

static function set($key, $value)

{self::$data[$key] = $value;

}}

MocktheSession


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Use different Storage strategies

Configuration becomes natural

Wrap third-party classes (Interface / Adapter)

Mock the Storage object (for testing)

Easy without changing the User class


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Dependency Injection is where

components are given their dependencies

through their constructors, methods, ordirectly into fields.

http://www.picocontainer.org/injection.html


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$storage = new SessionStorage();

// constructor injection$user = new User($storage);

// setter injection

$user = new User();$user->setStorage($storage);

// property injection

$user = new User();$user->storage = $storage;


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A slightly more complex

web example


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class Application{


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{function __construct(){

$this->request = new WebRequest();

$this->response = new WebResponse();

$storage = new FileSessionStorage('SESSION_ID');$this->user = new User($storage);

$cache = new FileCache(array('dir' => dirname(__FILE__).'/cache')

);$this->routing = new Routing($cache);

}

}

$application = new Application();


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Back to square 1

class Application{


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{function __construct(){

$this->request = new WebRequest();

$this->response = new WebResponse();

$storage = new FileSessionStorage('SESSION_ID');$this->user = new User($storage);

$cache = new FileCache(array('dir' => dirname(__FILE__).'/cache')

);$this->routing = new Routing($cache);

}

}

$application = new Application();


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We need a Container

Describes objects

and their dependencies

Instantiates and configures

objects on-demand


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A container

SHOULD be able to manage

ANY PHP object (POPO)

The objects MUST not know

that they are managed

by a container


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Parameters The SessionStorageInterface implementation we want to use (the class name) The session name

Objects SessionStorage User

Dependencies User depends on a SessionStorageInterface implementation


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Lets build a simple container with PHP 5.3


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DI Container

Managing parameters

class Container


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class Container{

protected $parameters = array();

public function setParameter($key, $value){

$this->parameters[$key] = $value;

}

public function getParameter($key){

return $this->parameters[$key];}

}

Decoupling


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$container = new Container();$container->setParameter('session_name', 'SESSION_ID');$container->setParameter('storage_class', 'SessionStorage');

$class = $container->getParameter('storage_class');$sessionStorage = new $class($container->getParameter('session_name'));

$user = new User($sessionStorage);

Decoup g

Customization

Objectscreation

class Container Using PHP


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class Container{

protected $parameters = array();

public function __set($key, $value){

$this->parameters[$key] = $value;

}

public function __get($key){

return $this->parameters[$key];}

}

UsingPHP

magicmethods

Interface


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$container = new Container();$container->session_name = 'SESSION_ID';$container->storage_class = 'SessionStorage';

$sessionStorage = new $container->storage_class($container->session_name);$user = new User($sessionStorage);

Int

iscleaner


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DI Container

Managing objects


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We need a way to describe how to create objects,

without actually instantiating anything!

Anonymous functions to the rescue!

Anonymous Functions / Lambdas


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y

A lambda is a function

defined on the fly

with no name

function () { echo 'Hello world!'; };



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y

A lambda can be stored

in a variable

$hello = function () { echo 'Hello world!'; };



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y

And then it can be used

as any other PHP callable

$hello();

call_user_func($hello);



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y

You can also pass a lambda

as an argument to a function or method

function foo(Closure $func){$func();

}

foo($hello);

Fonctions anonymes


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y$hello = function ($name) { echo 'Hello '.$name; };

$hello('Fabien');

call_user_func($hello, 'Fabien');

function foo(Closure $func, $name){

$func($name);}

foo($hello, 'Fabien');


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DI Container

Managing objects

class Container{protected $parameters = array();protected $objects array();


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protected $objects = array();

public function __set($key, $value){

$this->parameters[$key] = $value;}

public function __get($key){

return $this->parameters[$key];

}

public function setService($key, Closure $service){

$this->objects[$key] = $service;}

public function getService($key){

return $this->objects[$key]($this);}

}

Storealambda

abletocreatethe

objecton-demand

Asktheclosuretocreatetheobjectandpassthe

currentContainer

$container = new Container();$container >session name = 'SESSION ID';

Description


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$container->session_name = SESSION_ID ;$container->storage_class = 'SessionStorage';$container->setService('user', function ($c)

{return new User($c->getService('storage'));

});$container->setService('storage', function ($c){

return new $c->storage_class($c->session_name);});

$user = $container->getService('user');

CreatingtheUserisnowaseasyasbefore

Descrip

class Container{

protected $values array(); Simplifythecode


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protected $values = array();

function __set($id, $value)

{ $this->values[$id] = $value;}

function __get($id){

if (is_callable($this->values[$id])){

return $this->values[$id]($this);}else{

return $this->values[$id];}

}}

Simplify

$container = new Container();$container >session name = 'SESSION ID';

Unifiedinterface


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$container->session_name = SESSION_ID ;$container->storage_class = 'SessionStorage';$container->user = function ($c){

return new User($c->storage);};$container->storage = function ($c)

{return new $c->storage_class($c->session_name);

};

$user = $container->user;


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DI Container

Scope


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For some objects, like the user,

the container must alwaysreturn the same instance


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spl_object_hash($container->user)

!==spl_object_hash($container->user)

$container->user = function ($c)


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$container->user = function ($c){

static $user;

if (is_null($user)){

$user = new User($c->storage);}

return $user;};


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spl_object_hash($container->user)

===spl_object_hash($container->user)


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$container->user = $container->asShared(function ($c){

return new User($c->storage);});


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A closure is a lambda

that remembers the contextof its creation

class Article{

( )


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public function __construct($title){

$this->title = $title;}

public function getTitle(){

return $this->title;}

}

$articles = array(new Article('Title 1'),new Article('Title 2'),

);


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$mapper = function ($article){

return $article->getTitle();

};

$titles = array_map($mapper, $articles);


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$method = 'getTitle';

$mapper = function ($article) use($method){

return $article->$method();

};

$method = 'getAuthor';

$titles = array_map($mapper, $articles);


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$mapper = function ($method){

return function ($article) use($method){

return $article->$method();};

};


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$titles = array_map($mapper('getTitle'), $articles);

$authors = array_map($mapper('getAuthor'), $articles);


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$container->user = $container->asShared(function ($c){

return new User($c->storage);});

function asShared(Closure $lambda){


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return function ($container) use ($lambda)

{static $object;

if (is_null($object)){

$object = $lambda($container);}

return $object;};}

class Container{protected $values = array();

function set($id $value)


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function __set($id, $value){

$this->values[$id] = $value;

}


if (!isset($this->values[$id])){

throw new InvalidArgumentException(sprintf('Value "%s" is not defined.', $id));

}




}}

Errormanagement

class Container

{protected $values = array();

function __set($id, $value){

$this->values[$id] = $value;


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}


if (!isset($this->values[$id])){throw new InvalidArgumentException(sprintf('Value "%s" is not defined.', $id));

}




}

function asShared($callable){

return function ($c) use ($callable){

static $object;

if (is_null($object)){

$object = $callable($c);}return $object;

};}

}

40LOCforafully-

featuredcontainer

Im NOT advocating


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g

the usage of lambdas everywhere

This presentation is about

showing how they work

on practical examples


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A DI Container

does NOT manage

ALL your objects


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Good rule of thumb:It manages Global objects

Objects with only one instance (!= Singletons)


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LIKE

a User, a Request,

a database Connection, a Logger,


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UNLIKE

Model objects (a Product, a blog Post, )


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Symfony Components



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Rock-solid implementation of a DIC in PHP 5.3


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At the core of the Symfony 2.0 framework

which is one of the fastest framework


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Very flexible

Configuration in PHP, XML, YAML, or INI

$container = new Builder();


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$container = new Builder();

$container->register('output', 'FancyOutput');$container->

register('message', 'Message')->setArguments(array(

new sfServiceReference('output'),array('with_newline' => true)

));

$container->message->say('Hello World!');


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services:output: { class: FancyOutput }message:

class: Message

arguments:- @output- { with_newline: true }


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true


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imports:- { resource: parameters.yml }- { resource: parameters.ini }- { resource: services.xml }


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As fast as it can be

The container can be

compiled down

to plain PHP code

use Symfony\Components\DependencyInjection\Container;use Symfony\Components\DependencyInjection\Reference;use Symfony\Components\DependencyInjection\Parameter;

class ProjectServiceContainer extends Container{


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{protected $shared = array();

protected function getOutputService(){

if (isset($this->shared['output'])) return $this->shared['output'];

$instance = new FancyOutput();

return $this->shared['output'] = $instance;}

protected function getMessageService(){

if (isset($this->shared['message'])) return $this->shared['message'];

$instance = new Message($this->getOutputService(), array('with_newline' => true));

return $this->shared['message'] = $instance;}

}


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Semantic configuration

Thanks to an extension mechanism


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p y y p j g

fabien.potencierxxxxxx


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xmlns:doctrine="http://www.symfony-project.org/schema/dic/doctrine" xmlns:zend="http://www.symfony-project.org/schema/dic/zend"

xsi:schemaLocation="http://www.symfony-project.org/schema/dic/services http://www.symfony-project.org/schema/dic/services/services-1.0.xsd

http://www.symfony-project.org/schema/dic/doctrine http://www.symfony-project.org/schema/dic/doctrine/doctrine-1.0.xsd

http://www.symfony-project.org/schema/dic/swiftmailer http://www.symfony-project.org/schema/dic/swiftmailer/swiftmailer-1.0.xsd" >

fabien.potencierxxxxxx

auto-completion

andvalidation

withXSD

zend.logger:level: debug


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level: debug

path: %kernel.root_dir%/logs/%kernel.environment%.log

doctrine.dbal:dbname: dbnameusername: root

password: ~

swift.mailer:transport: gmailusername: fabien.potencier

password: xxxxxxx


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Everything is converted by the extension

to plain services and parametersno overhead

Loader::registerExtension(new SwiftMailerExtension());Loader::registerExtension(new DoctrineExtension());Loader::registerExtension(new ZendExtension());


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Loader::registerExtension(new ZendExtension());

$loader = new XmlFileLoader(__DIR__);$config = $loader->load('services.xml');

$container = new Builder();$container->merge($config);

$container->mailer->...

$dumper = new PhpDumper($container);echo $dumper->dump();

More about Dependency Injection

http://fabien.potencier.org/article/17/on-php-5-3-lambda-functions-and-closures


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http://components.symfony-project.org/dependency-injection/ (5.2)

http://github.com/fabpot/symfony/tree/master/src/Symfony/Components/DependencyInjection/(5.3)

http://github.com/fabpot/pimple

http://twittee.org/


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Remember, most of the time,

you dont need a Container

to use Dependency Injection


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You can start to use and benefit from

Dependency Injection today

by implementing it


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y p g

in your projects

by using externals librariesthat already use DI

without the need of a container

Symfony


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y y

Zend FrameworkezComponents

DoctrineSwift Mailer


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Questions?

My slides will be available on

slideshare.com/fabpot

Sensio S.A.

92 98 boulevard Victor Hugo


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92-98, boulevard Victor Hugo

92 115 Clichy CedexFRANCE

Tl. : +33 1 40 99 80 80

Contact

Fabien Potencierfabien.potencier at sensio.com

http://www.sensiolabs.com/

http://www.symfony-project.org/

http://fabien.potencier.org/

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Dependency Injection Zendcon 2010 101104172213 Phpapp01