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Decoupling from the framework Jakub Zalas 7th of April 2014

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@jakzal @jakub_zalas @SensioLabsUK £  

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COUPLING

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"MODULES ARE COUPLED IF CHANGING ONE OF THEM REQUIRES CHANGING ANOTHER ONE." http://martinfowler.com/ieeeSoftware/coupling.pdf Martin Fowler

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tight coupling loose coupling

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COUPLING AND COHESION

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tight coupling low cohesion

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loose coupling high cohesion

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WHY IS TIGHT COUPLING BAD?

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WHY IS LOOSE COUPLING GOOD?

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REUSABILITY

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READABILITY

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MAINTENANCE

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CHANGE

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LOOSEN UP? How to

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MAKE DEPENDENCIES EXPLICIT

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class PackageCrawler { public function crawl($resource) { $browser = Browser::getInstance(); $response = $browser->get($resource); // @todo parse } }

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use Buzz\Browser; class PackageCrawler { public function crawl($resource) { $browser = new Browser(); $response = $browser->get($resource); // @todo parse } }

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DEPENDENCY INJECTION !

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use Buzz\Browser; class PackageCrawler { private $browser; public function __construct(Browser $browser) { $this->browser = $browser; } public function crawl($resource) { $response = $this->browser->get($resource); // @todo parse } }

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INJECT EXACTLY WHAT YOU NEED

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use Buzz\Browser; class PackageCrawler { private $browser; public function __construct(Browser $browser) { $this->browser = $browser; } public function crawl($resource, Container $container) { $user = $container->get('security.context') ->getToken()->getUser(); $response = $this->browser->get( $resource, array('X-User' => $user->getId()) ); // @todo parse } }

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https://twitter.com/iamtankist/status/359382451816112129

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use Buzz\Browser; class PackageCrawler { private $browser; public function __construct(Browser $browser) { $this->browser = $browser; } public function crawl($resource, $userId) { $response = $this->browser->get( $resource, array('X-User' => $userId) ); // @todo parse } }

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DON'T MIX LAYERS

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use Buzz\Browser; use Symfony\Component\Console\Input\InputInterface; class PackageCrawler { private $browser; public function __construct(Browser $browser) { $this->browser = $browser; } public function crawl(InputInterface $input) { $response = $this->browser->get( $input->getOption('resource') ); // @todo parse } }

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use Buzz\Browser; class PackageCrawler { private $browser; public function __construct(Browser $browser) { $this->browser = $browser; } public function crawl($resource) { $response = $this->browser->get( $resource ); // @todo parse } }

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BI-DIRECTIONAL DEPENDENCIES ARE A SMELL

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BREAK DEPENDENCIES

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use Buzz\Browser; class PackageCrawler { private $browser; public function __construct(Browser $browser) { $this->browser = $browser; } public function crawl($resource) { $response = $this->browser->get($resource); // @todo parse } }

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interface HttpClient { public function get($resource, array $headers = []); }

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class PackageCrawler { private $httpClient; public function __construct(HttpClient $httpClient) { $this->httpClient = $httpClient; } public function crawl($resource) { $response = $this->httpClient->get($resource); // @todo parse } }

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use Buzz\Browser; class BuzzClient implements HttpClient { private $browser; public function __construct(Browser $browser) { $this->browser = $browser; } public function get($resource, array $headers) { return (string) $this->browser->get( $resource, $headers ); } }

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use Guzzle\Client; class GuzzleClient implements HttpClient { private $guzzle; public function __construct(Client $guzzle) { $this->guzzle = $guzzle; } public function get($resource, array $headers) { $request = $this->guzzle->createRequest( 'GET', $resource ); $response = $request->send(); return $response->getBody(); } }

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DEFER DECISIONS

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DEFER COMMITMENT

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FRAMEWORK?

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use Symfony\Bundle\FrameworkBundle\Controller\Controller; class SearchController extends Controller { public function searchAction(Request $request) { $keywords = $request->query->get('keywords'); $products = $this->getDoctrine() ->getRepository('Acme:Product') ->search($keywords); return $this->render( 'template.html.twig', array('products' => $products) ); } }

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LAYERED ARCHITECTURE

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https://www.goodreads.com/book/show/179133.Domain_driven_Design

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CLEAN ARCHITECTURE

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http://blog.8thlight.com/uncle-bob/2012/08/13/the-clean-architecture.html

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SOURCE CODE DEPENDENCIES CAN ONLY POINT INWARDS

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HEXAGONAL ARCHITECTURE a.k.a. PORTS AND ADAPTERS

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Application Doctrine In memory UI Tests CLI

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"Create your application to work without either a UI or a database […]" http://alistair.cockburn.us/Hexagonal+architecture

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UI IS AN IMPLEMENTATION DETAIL

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DATABASE IS AN IMPLEMENTATION DETAIL

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FRAMEWORK IS AN IMPLEMENTATION DETAIL

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STEP 0 MAKE DEPENDENCIES EXPLICIT

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use Doctrine\Common\Persistence\ManagerRegistry; use Symfony\Bundle\FrameworkBundle\Templating\EngineInterface; class SearchController { private $templating; private $doctrine; public function __construct( EngineInterface $templating, ManagerRegistry $doctrine ) { $this->templating = $templating; $this->doctrine = $doctrine; } }

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// .. class SearchController { // ... public function searchAction(Request $request) { $keywords = $request->query->get('keywords'); $repository = $this->doctrine ->getRepository('Acme:Product') ->search($keywords); return $this->templating->renderResponse( 'template.html.twig', array('products' => $products) ); } }

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STEP 1 ONLY INJECT WHAT YOU ACTUALLY NEED

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use Doctrine\Common\Persistence\ManagerRegistry; use Symfony\Bundle\FrameworkBundle\Templating\EngineInterface; class SearchController { private $templating; private $doctrine; public function __construct( EngineInterface $templating, ManagerRegistry $doctrine ) { $this->templating = $templating; $this->doctrine = $doctrine; } }

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use Acme\ProductBundle\Entity\ProductRepository; use Symfony\Bundle\FrameworkBundle\Templating\EngineInterface; class SearchController { private $templating; private $repository; public function __construct( EngineInterface $templating, ProductRepository $repository ) { $this->templating = $templating; $this->repository = $repository; } }

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// .. class SearchController { // ... public function searchAction(Request $request) { $keywords = $request->query->get('keywords'); $repository = $this->repository->search($keywords); return $this->templating->renderResponse( 'template.html.twig', array('products' => $products) ); } }

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STEP 2 DON'T TALK TO THE INFRASTRUCTURE DIRECTLY

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namespace Acme\ProductCatalog; interface ProductRepository { /** * @param string $keywords * * @return Product[] */ public function search($keywords); }

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use Acme\ProductCatalog\ProductRepository; use Symfony\Bundle\FrameworkBundle\Templating\EngineInterface; class SearchController { private $templating; private $repository; public function __construct( EngineInterface $templating, ProductRepository $repository ) { $this->templating = $templating; $this->repository = $repository; } }

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DON'T FOLLOW THE FRAMEWORK

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$this->getDoctrine() ->getRepository('Acme:product') ->find($keywords);

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MAKE IT OPTIONAL

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A GOOD FRAMEWORK WILL HELP YOU

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$this->repository->search($keywords); Acme:Product

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DON'T START WITH THE FRAMEWORK

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MAKE YOUR APPLICATION INDEPENDENT

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AND THEN INTEGRATE IT WITH THE FRAMEWORK

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REMEMBER!

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TDD IS YOUR FRIEND

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THANK YOU!

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Credits