Real World Dependency Injection - PFCongres 2010

Real World Dependency Injection
Stephan Hochdörfer, bitExpert AG

"Dependency Injection is a key element of agile architecture"
Ward Cunningham

About me
 Founder of bitExpert AG, Mannheim

 Field of duty

Department Manager of Research Labs

Head of Development for bitFramework

 Focusing on

PHP

Generative Programming


Contact me

@shochdoerfer

S.Hochdoerfer@bitExpert.de

Agenda
1. What is Dependency Injection?

2. Real World examples

3. Pros & Cons

4. Questions

What is Dependency Injection?

"Dependency Injection is probably one of the most dead simple
design pattern [...] but it is also one of the most difficult one to
explain well."
Fabien Potencier



 Popularized by Martin Fowler in 2004

 Technique for supplying external dependencies to a component

 Main idea: Ask for things, do not look for things!

 Three elements

Dependant / Consumer

Dependencies, e.g. service objects

Injector / Container


Problems of Dependencies

 Code is very tightly coupled

Hard to re-use code

Hard to test code, no isolation possible

 Difficult to maintain

What is affected when code changes?

Boilerplate configuration code within Business logic


Simple Dependency

Main Required
class class


Complex Dependency

Required
class
Main Required
class class
Required
class


Very complex Dependency
Database

Required
class
External
Main Required
resource
class class
Required
class

Required Required
Webservice
class class


How to Manage Dependencies?


How to Manage Dependencies?

You don`t need to. The Framework does it all!


Types of Dependency Injection

Type 1: Interface injection

<?php

class MySampleService implements IMySampleService, IApplicationContextAware
{
/**
* @var IApplicationContext
*/
private $oCtx;

public function setApplicationContext(IApplicationContext $poCtx) {
$this->oCtx = $poCtx;
}
}
?>



Type 2: Setter injection

<?php

class MySampleService implements IMySampleService {
/**
* @var ISampleDao
*/
private $oSampleDao;

public function setSampleDao(ISampleDao $poSampleDao) {
$this->oSampleDao = $poSamleDao;
}
}
?>



Type 3: Constructor injection

<?php

/**
* @var ISampleDao
*/

public function __construct(ISampleDao $poSampleDao) {
}
}
?>


Configuration Types

Type 1: Annotations

<?php

/**
* @var ISampleDao
*/

/**
* @Inject
*/
}
}
?>


Configuration Types

Type 2: External configuration via XML, JSON, YAML, ...

<?xml version="1.0" encoding="UTF-8" ?>
<beans xmlns="http://www.bitexpert.de/schema"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.bitexpert.de/schema/
http://www.bitexpert.de/schema/bitFramework-beans.xsd">

<bean id="SampleDao" class="SampleDao">
<constructor-arg value="app_sample" />
<constructor-arg value="iSampleId" />
<constructor-arg value="BoSample" />
</bean>

<bean id="SampleService" class="MySampleService">
<constructor-arg ref="SampleDao" />
</bean>
</beans>


Configuration Types

Type 3: PHP Configuration

<?php
class BeanCache extends bF_Beanfactory_Container_PHP_ACache {
protected function createSampleDao() {
$oBean = new SampleDao('app_sample', 'iSampleId', 'BoSample');
return array("oBean" => $oBean, "bSingleton" => "1");
}

protected function createMySampleService() {
$oBean = new MySampleService($this->getBean('SampleDao'));
return array("oBean" => $oBean, "bSingleton" => "1");
}
?>

Real world examples

"High-level modules should not depend on low-level modules.
Both should depend on abstractions."
Robert C. Martin

Real World examples

Unittesting made easy

<?php
require_once 'PHPUnit/Framework.php';

class ServiceTest extends PHPUnit_Framework_TestCase {
public function testSampleService() {
$oSampleDao = $this->getMock('ISampleDao');

// run test case
$oService = new MySampleService($oSampleDao);
$bReturn = $oService->doWork();

// check assertions
$this->assertTrue($bReturn);
}
}
?>

Real World examples

One class, multiple configurations

Implementation

Live Working


<bean id="ExportLive" class="MyApp_Service_ExportManager">
<constructor-arg ref="DAOPageLive" />
</bean>

<bean id="ExportWorking" class="MyApp_Service_ExportManager">
<constructor-arg ref="DAOPageWorking" />
</bean>

</beans>

Real World examples

Mocking external services

Consumer Connector Webservice

IConnector interface


<bean id="Consumer" class="MyApp_Service_Consumer">
<constructor-arg ref="Connector" />
</bean>

</beans>

Real World examples

Mocking external services

alternative Local
Consumer
Connector filesystem

IConnector interface


<bean id="Consumer" class="MyApp_Service_Consumer">
<constructor-arg ref="AltConnector" />
</bean>

</beans>

Real World examples

Clean, readable code
<?php

class Promio_Action_News_Delete extends bF_Mvc_Action_AAction {
/**
* @var Promio_Service_INewsManager
*/
private $oNewsManager;

public function __construct(Promio_Service_INewsManager $poNewsManager) {
$this->oNewsManager = $poNewsManager;
}

protected function execute(bF_Mvc_Request $poRequest) {
try {
$this->oNewsManager->delete((int) $poRequest->getVar('iNewsId'));
}
catch(bF_Service_ServiceException $oException) {
}

$oMaV = new bF_Mvc_ModelAndView($this->getSuccessView(), true);
return $oMaV;
}
}
?>

Real World examples

No framework dependency
<?php

/**
* @var ISampleDao
*/

}

public function getSample($piSampleId) {
try {
return $this->oSampleDao->readByPrimaryKey((int) $piSampleId);
}
catch(DaoException $oException) {
}
}
}
?>

Real World examples

Cache, Cache, Cache!
180

160

140

120

100

80

60

40

20

0
XML no Caching XML with Caching PHP PHP compiled

Requests per Second meassured via Apache HTTP server benchmarking tool

Agenda

2. Real World Examples

3. Pros & Cons

4. Questions

Pros & Cons

Benefits

 Good for agile development

Reducing amount of code

Helpful for Unit testing

 Loose coupling

Least intrusive mechanism

Switching implementations by changing configuration

 Clean view on the code

Separate configuration from code

Getting rid of boilerpate configuration code

Pros & Cons

Cons

 To many different implementations, no standard today!

Bucket, Crafty, FLOW3, Imind_Context, PicoContainer,
Pimple, Phemto, Stubbles, Symfony 2.0, Sphicy, Solar,
Substrate, XJConf, Yadif, Zend_Di (Proposal), Lion
Framework, Spiral Framework, Xyster Framework, …

No JSR 330 for PHP

 Simple Containers vs. fully-stacked Framework

No dependency from application to Container!

 Developers need to be aware of configuration ↔ runtime

Agenda

2. Pros & Cons

3. Real World examples

4. Questions

Real World Dependency Injection - PFCongres 2010

Real World Dependency Injection - PFCongres 2010

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