Separation of concerns - DPC12

Separation of Concerns

Separation of concerns

About Joshua

Joshua Thijssen, NoxLogic / Techademy

Freelance Consultant, Developer, Trainer

Development in PHP, Python, Perl, C, Java

[email protected]

@jaytaph


About Stephan

Stephan Hochdörfer, bitExpert AG

Department Manager Research Labs

enjoying PHP since 1999

[email protected]

@shochdoerfer


It is what I sometimes have called the separation of concerns, which [...] is

yet the only available technique for effective ordering of one's thoughts.

Edsger W. Dijkstra, "On the role of scientific thought" (1974)


SoC […] is the process of breaking a computer program into distinct

features that overlap in functionality as little as possible.

http://en.wikipedia.org/wiki/Separation_of_concerns


It`s all about focusing!


One step a time. Focus on the details!


<?php$items = array();$token = file_get_contents("https://graph.facebook.com/oauth/access_token?...");$feed = file_get_contents("https://graph.facebook.com/ident/feed?".$token);$feed = json_decode($feed, true);foreach($feed['data'] as $post) { if('123456789012' === $post['from']['id']) { $items[] = array( 'date' => strtotime($post['created_time']), 'message' => $post['message']); }}

$feed = file_get_contents("http://search.twitter.com/search.json?q=from:ident");$feed = json_decode($feed, true);foreach($feed['results'] as $tweet) { $items[] = array( 'date' => strtotime($tweet['created_at']), 'message' => $tweet['text']);}

foreach($items as $item) { echo $item['message'];}




foreach($items as $item) { echo $item['message'];}}

Controller part!




foreach($items as $item) { echo $item['message'];}

View part!


Very unstable. Not safe for changes....


„Make everything as simple as possible...“


Establish boundaries


What are the boundaries?

Presentation Layer



Presentation Layer

Business Layer



Presentation Layer

Business Layer

Resource Access Layer

Isolate functionality, break it apart!



<?phpnamespace Acme\DemoBundle\Controller;use Symfony\Bundle\FrameworkBundle\Controller\Controller;use Sensio\Bundle\FrameworkExtraBundle\Configuration\Route;use Sensio\Bundle\FrameworkExtraBundle\Configuration\Template;

class DemoController extends Controller { /** * @Route("/", name="_demo") * @Template() */ public function indexAction() {

$items = array();$token = file_get_contents("https://graph.facebook.com/oauth/access_to...");$feed = file_get_contents("https://graph.facebook.com/ident/feed?".$token);$feed = json_decode($feed, true);foreach($feed['data'] as $post) { if('123456789012' === $post['from']['id']) { $items[] = array( 'date' => strtotime($post['created_time']), 'message' => $post['message']); }}


$feed = file_get_contents("http://search.twitter.com/search.json?...");$feed = json_decode($feed, true);foreach($feed['results'] as $tweet) { $items[] = array( 'date' => strtotime($tweet['created_at']), 'message' => $tweet['text']);}

return array('items' => $items); }}

Focus on one responsibility a time!





$items = array();$token = file_get_contents("https://graph.facebook.com/oauth/access_to...");$feed = file_get_contents("https://graph.facebook.com/ident/feed?".$token);$feed = json_decode($feed, true);foreach($feed['data'] as $post) { if('123456789012' === $post['from']['id']) { $items[] = array( 'date' => strtotime($post['created_time']), 'message' => $post['message']); }}

Facebook connector




Twitter connector

Interfaces as a contract



<?phpinterface ConnectorInterface { /** * Will return an array of the latest posts. * return array */ public function getLatestPosts() { }}


<?phpclass FacebookConnector implements ConnectorInterface { protected $handle; public function __construct($handle) { $this->handle = $handle; } public function getLatestPosts() { $items = array(); $token = file_get_contents("https://graph.facebook.com/oauth/access..."); $feed = file_get_contents("https://graph.facebook.com/.

$this->handle."/feed?".$token); $feed = json_decode($feed, true); foreach($feed['data'] as $post) { if('123456789012' === $post['from']['id']) {

$items[] = array( 'date' => strtotime($post['created_time']), 'message' => $post['message']);

} } return $items; }}


<?phpclass FacebookConnector implements ConnectorInterface { protected $handle; public function __construct($handle) { $this->handle = $handle; } public function getLatestPosts() { $token = $this->getAccessToken(); return $this->readPosts($token); }

protected function getAccessToken() { return file_get_contents("https://graph.facebook.com/oauth/access_?..."); }

protected function readPosts($token) { // read the post, filter all relevant and return them... }}


<?phpclass FacebookConnectorV2 extends FacebookConnector {

protected function getAccessToken() { return md5($this->handle); }}

Easy to extend, will not influence the behaviour of other methods!




$items = array();$fb = $this->get('FbConnector');$items += $fb->getLatestPosts();





$items = array();$fb = $this->get('FbConnector');$items += $fb->getLatestPosts();

$twitter = $this->get('TwitterConnector');$items += $twitter->getLatestPosts();


Will improve the testability!


Will reduce tight coupling!


Will increase component reuse!


The value of separation

Why should I do it?



1. Getting rid of code duplication



2. Application becomes more stableand easier to understand



3. Single responsibility offers clear extension points



4. Increases the reusability of components



How to separate the concerns?


How to separate? Horizontal Separation

Presentation Layer

Business Layer



How to separate? Horizontal Separation

./symfony |-app |---cache |---config |---Resources |-src |---Acme |-----DemoBundle |-------Controller |-------Resources |---------config |---------public |-----------css |-----------images |---------views |-----------Demo |-----------Welcome |-------Tests |---------Controller |-web


How to separate? Service Separation

Service Interface Layer

Business Layer



How to separate? Service Separation

Frontend / UI Webservers

REST API

Datastore

Solr Search Service


How to separate? Vertical Separation

ModuleA ModuleB ModuleC



./symfony |-app |---cache |---config |---Resources |-src |---Acme |-----AdminBundle |-------Controller |-------Resources |-------Tests |-----ProductsBundle |-------Controller |-------Resources |-------Tests |-----CustomersBundle |-------Controller |-------Resources |-------Tests |-web



PresentationLayer

BusinessLayer

ResourceAccess Layer

PresentationLayer

BusinessLayer


PresentationLayer

BusinessLayer




./symfony |-app |---cache |---config |---Resources |-src |---Acme |-----AdminBundle |-------Controller |-------Resources |-------Tests |-----ProductsBundle |-------Controller |-------Resources |-------Tests |-----CustomersBundle |-------Controller |-------Resources |-------Tests |-web

Cross-cutting concerns?

How to deal with security or logging aspects?



How to separate? Aspect Separation

Presentation Layer

Business Layer


Aspects


How to separate? Aspect Separation<?phpnamespace Acme\Products\Aspects;

/** * @FLOW3\Aspect */class LoggingAspect { /** * @FLOW3\Inject * @var \Acme\Logger\LoggerInterface */ protected $logger;

/** * @param \TYPO3\FLOW3\AOP\JoinPointInterface $joinPoint * @FLOW3\Before("method(Acme\Products\Model\Product->delete())") */ public function log(\TYPO3\FLOW3\AOP\JoinPointInterface $jp) { $product = $jp->getMethodArgument('product'); $this->logger->info('Removing ' . $product->getName()); }}


Dependency Direction


Dependency Direction

"High-level modules should not depend on low-level modules.

Both should depend on abstractions."

Robert C. Martin


Inverting Concerns

PresentationLayer

BusinessLayer



Inverting Concerns

PresentationLayer

BusinessLayer


PresentationLayer

BusinessLayer


UIComponent


Inverting Concerns

The goal of Dependency Injection is to separate the concerns of

obtaining the dependencies from the core concerns of a component.


What are the benefits? Let`s recap....


What are the benefits?

1. Facilitate reusability



2. Ensure the maintainability



3. Increasing the code quality



4. Enables everyone to understand the application



5. Allows developers to work on components in isolation

Thank you!

http://joind.in/6244

Technology

Separation of concerns - DPC12