This document discusses dependency injection and provides examples of its use. It begins with an introduction to dependency injection, explaining that it is a technique for supplying external dependencies to a component. It then provides examples of how dependency injection can be used to make unit testing easier, configure one class for multiple uses, and mock external services. Benefits include loose coupling and clean separation of configuration from code, while drawbacks include a lack of standardization and potential framework dependencies. Real-world examples demonstrate how dependency injection improves code readability, enables caching, and avoids tight coupling.

1. Real World Dependency Injection
Stephan Hochdörfer, bitExpert AG
"Dependency Injection is a key element of agile architecture"
Ward Cunningham

2. 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

3. Agenda
1. What is Dependency Injection?
2. Real World examples
3. Pros & Cons
4. Questions

4. 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

5. 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

6. What is Dependency Injection?
What is Dependency Injection?
 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

7. What is Dependency Injection?
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

8. What is Dependency Injection?
Simple Dependency
Main Required
class class

9. What is Dependency Injection?
Complex Dependency
Required
class
Main Required
class class
Required
class

10. What is Dependency Injection?
Very complex Dependency
Database
Required
class
External
Main Required
resource
class class
Required
class
Required Required
Webservice
class class

11. What is Dependency Injection?
Very complex Dependency
Database
Required
class
External
Main Required
resource
class class
Required
class
Required Required
Webservice
class class

12. What is Dependency Injection?
Very complex Dependency
Database
Required
class
External
Main Required
resource
class class
Required
class
Required Required
Webservice
class class

13. What is Dependency Injection?
How to Manage Dependencies?

14. What is Dependency Injection?
How to Manage Dependencies?
You don`t need to. The Framework does it all!

15. What is Dependency Injection?
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;
}
}
?>

16. What is Dependency Injection?
Types of Dependency Injection
Type 2: Setter injection
<?php
class MySampleService implements IMySampleService {
/**
* @var ISampleDao
*/
private $oSampleDao;
public function setSampleDao(ISampleDao $poSampleDao) {
$this->oSampleDao = $poSamleDao;
}
}
?>

17. What is Dependency Injection?
Types of Dependency Injection
Type 3: Constructor injection
<?php
class MySampleService implements IMySampleService {
/**
* @var ISampleDao
*/
private $oSampleDao;
public function __construct(ISampleDao $poSampleDao) {
$this->oSampleDao = $poSamleDao;
}
}
?>

18. What is Dependency Injection?
Configuration Types
Type 1: Annotations
<?php
class MySampleService implements IMySampleService {
/**
* @var ISampleDao
*/
private $oSampleDao;
/**
* @Inject
*/
public function __construct(ISampleDao $poSampleDao) {
$this->oSampleDao = $poSamleDao;
}
}
?>

19. What is Dependency Injection?
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>

20. What is Dependency Injection?
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");
}
?>

21. Agenda
1. What is Dependency Injection?
2. Real World examples
3. Pros & Cons
4. Questions

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

23. 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);
}
}
?>

24. Real World examples
One class, multiple configurations
Implementation
Live Working
<?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="ExportLive" class="MyApp_Service_ExportManager">
<constructor-arg ref="DAOPageLive" />
</bean>
<bean id="ExportWorking" class="MyApp_Service_ExportManager">
<constructor-arg ref="DAOPageWorking" />
</bean>
</beans>

25. Real World examples
Mocking external services
Consumer Connector Webservice
IConnector interface
<?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="Consumer" class="MyApp_Service_Consumer">
<constructor-arg ref="Connector" />
</bean>
</beans>

26. Real World examples
Mocking external services
alternative Local
Consumer
Connector filesystem
IConnector interface
<?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="Consumer" class="MyApp_Service_Consumer">
<constructor-arg ref="AltConnector" />
</bean>
</beans>

27. 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;
}
}
?>

28. Real World examples
No framework dependency
<?php
class MySampleService implements IMySampleService {
/**
* @var ISampleDao
*/
private $oSampleDao;
public function __construct(ISampleDao $poSampleDao) {
$this->oSampleDao = $poSamleDao;
}
public function getSample($piSampleId) {
try {
return $this->oSampleDao->readByPrimaryKey((int) $piSampleId);
}
catch(DaoException $oException) {
}
}
}
?>

29. 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

30. Agenda
1. What is Dependency Injection?
2. Real World Examples
3. Pros & Cons
4. Questions

31. 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

32. 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

33. Agenda
1. What is Dependency Injection?
2. Pros & Cons
3. Real World examples
4. Questions