Separation of concerns - DPC12

Separation of concerns

About Joshua

 Joshua Thijssen, NoxLogic / Techademy
 Freelance Consultant, Developer, Trainer
 Development in PHP, Python, Perl, C, Java
 jthijssen@noxlogic.nl
 @jaytaph


About Stephan

 Stephan Hochdörfer, bitExpert AG
 Department Manager Research Labs
 enjoying PHP since 1999
 S.Hochdoerfer@bitExpert.de
 @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']);
}
}

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

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


<?php Controller part!
$items = array();
if('123456789012' === $post['from']['id']) {
$items[] = array(
}
}

$items[] = array(
}

}}


<?php
$items = array();
if('123456789012' === $post['from']['id']) {
$items[] = array(
}
}

$items[] = array(
}

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!


<?php
namespace AcmeDemoBundleController;
use SymfonyBundleFrameworkBundleControllerController;
use SensioBundleFrameworkExtraBundleConfigurationRoute;
use SensioBundleFrameworkExtraBundleConfigurationTemplate;

class DemoController extends Controller {
/**
* @Route("/", name="_demo")
* @Template()
*/
public function indexAction() {
$items = array();
$token = file_get_contents("https://graph.facebook.com/oauth/access_to...");
if('123456789012' === $post['from']['id']) {
$items[] = array(
}
}


$feed = file_get_contents("http://search.twitter.com/search.json?...");
$items[] = array(
}

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


Focus on one responsibility a time!


<?php

/**
* @Template()
*/
$items = array();
Facebook connector
$token = file_get_contents("https://graph.facebook.com/oauth/access_to...");
if('123456789012' === $post['from']['id']) {
$items[] = array(
}
}


Twitter connector
$items[] = array(
}

}
}


Interfaces as a contract


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


<?php
class FacebookConnector implements ConnectorInterface {
protected $handle;

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

$items = array();
$token = file_get_contents("https://graph.facebook.com/oauth/access...");
$feed = file_get_contents("https://graph.facebook.com/.
$this->handle."/feed?".$token);
if('123456789012' === $post['from']['id']) {
$items[] = array(
}
}
return $items;
}
}


<?php
class FacebookConnector implements ConnectorInterface {
protected $handle;

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

$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...
}
}


<?php
class FacebookConnectorV2 extends FacebookConnector {

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

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


<?php

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

$items[] = array(
}


<?php

/**
* @Template()
*/
$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 stable
and 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? Service Separation

Service Interface Layer

Business Layer



How to separate? Service Separation

Frontend / UI Webservers

REST API Solr Search Service

Datastore


How to separate? Vertical Separation

Module A Module B Module C



Presentation Presentation Presentation
Layer Layer Layer

Business Business Business
Layer Layer Layer

Resource Resource Resource
Access Layer Access Layer Access Layer


Cross-cutting concerns?

How to deal with security or logging
aspects?


How to separate? Aspect Separation

Aspects
Presentation Layer

Business Layer



How to separate? Aspect Separation
<?php
namespace AcmeProductsAspects;

/**
* @FLOW3Aspect
*/
class LoggingAspect {
/**
* @FLOW3Inject
* @var AcmeLoggerLoggerInterface
*/
protected $logger;

/**
* @param TYPO3FLOW3AOPJoinPointInterface $joinPoint
* @FLOW3Before("method(AcmeProductsModelProduct->delete())")
*/
public function log(TYPO3FLOW3AOPJoinPointInterface $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

Presentation
Layer

Business
Layer

Resource
Access Layer


Inverting Concerns

Presentation UI Presentation
Layer Component Layer

Business Business
Layer Layer

Resource Resource
Access Layer Access Layer


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

Separation of concerns - DPC12

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Separation of concerns - DPC12