This document discusses dependency injection and its benefits. It defines dependencies as components that an application relies on. Hard-coded dependencies are problematic because they are tightly coupled, not reusable, difficult to test, and complicate development. Dependency injection solves these issues by injecting dependencies through interfaces rather than having components directly instantiate their dependencies. This allows for loose coupling, reuse, testability, and flexible configurations of classes.

1. Real World
Dependency Injection
Stephan Hochdörfer, bitExpert AG

2. Real World Dependency Injection
About me
 Stephan Hochdörfer, bitExpert AG
 Department Manager Research Labs
 enjoying PHP since 1999
 S.Hochdoerfer@bitExpert.de
 @shochdoerfer

3. Real World Dependency Injection
What are Dependencies?

4. Real World Dependency Injection
What are Dependencies?
Application
Framework add. Libraries

5. Real World Dependency Injection
What are Dependencies?
Controller
PHP extensions Service / Model Utils
Datastore(s)

6. Real World Dependency Injection
Are Dependencies bad?

7. Real World Dependency Injection
Are Dependencies bad?
Dependencies are not bad!
They are useful!

8. Real World Dependency Injection
Are Dependencies bad?
Hard-coded dependencies are bad!

9. Real World Dependency Injection
Tightly coupled code

10. Real World Dependency Injection
No reuse of components

11. Real World Dependency Injection
No isolation, not testable!

12. Real World Dependency Injection
Development gets overcomplicated!

13. Real World Dependency Injection
s
„new“ is evil!

14. Real World Dependency Injection
„new“ is evil!
<?php
class DeletePage extends Mvc_Action_AAction {
private $pageManager;
public function __construct() {
$this->pageManager = new PageManager();
}
protected function execute(Mvc_Request $request) {
$this->pageManager->delete(
(int) $request->get('pageId')
);
}
}

15. Real World Dependency Injection
„new“ is evil!
<?php
class DeletePage extends Mvc_Action_AAction {
private $pageManager;
public function __construct(PageManager $pm) {
$this->pageManager = $pm;
}
protected function execute(Mvc_Request $request) {
$this->pageManager->delete(
(int) $request->get('pageId')
);
}
}

16. Real World Dependency Injection
"High-level modules should not
depend on low-level modules.
Both should depend on
abstractions."
Robert C. Martin

17. Real World Dependency Injection
Interfaces act as contracts

18. Real World Dependency Injection
„new“ is evil!
<?php
class DeletePage extends Mvc_Action_AAction {
private $pageManager;
public function __construct(IPageManager $pm) {
$this->pageManager = $pm;
}
protected function execute(Mvc_Request $request) {
$this->pageManager->delete(
(int) $request->get('pageId')
);
}
}

19. Real World Dependency Injection
How to Manage Dependencies?

20. Real World Dependency Injection
Manually resolve dependencies?

21. Real World Dependency Injection
Automatic wiring required!
Simple Container vs. Full stacked
DI Framework

22. Real World Dependency Injection
What is Dependency Injection?

23. Real World Dependency Injection
What is Dependency Injection?
Consumer

24. Real World Dependency Injection
What is Dependency Injection?
Consumer Dependencies

25. Real World Dependency Injection
What is Dependency Injection?
Consumer Dependencies Container

26. Real World Dependency Injection
What is Dependency Injection?
Consumer Dependencies Container

27. Real World Dependency Injection
How to inject a Dependency?

28. Real World Dependency Injection
Constructor Injection
<?php
class MySampleService implements IMySampleService {
/**
* @var ISampleDao
*/
private $sampleDao;
public function __construct(ISampleDao $sampleDao) {
$this->sampleDao = $sampleDao;
}
}

29. Real World Dependency Injection
Setter injection
<?php
class MySampleService implements IMySampleService {
/**
* @var ISampleDao
*/
private $sampleDao;
public function setSampleDao(ISampleDao $sampleDao){
$this->sampleDao = $sampleDao;
}
}

30. Real World Dependency Injection
Interface injection
<?php
interface IApplicationContextAware {
public function setCtx(IApplicationContext $ctx);
}

31. Real World Dependency Injection
Interface injection
<?php
class MySampleService implements IMySampleService,
IApplicationContextAware {
/**
* @var IApplicationContext
*/
private $ctx;
public function setCtx(IApplicationContext $ctx) {
$this->ctx = $ctx;
}
}

32. Real World Dependency Injection
How to wire it all up?

33. Real World Dependency Injection
Annotation based wiring
<?php
class MySampleService implements IMySampleService {
private $sampleDao;
/**
* @Inject
*/
public function __construct(ISampleDao $sampleDao)
{
$this->sampleDao = $sampleDao;
}
}

34. Real World Dependency Injection
Annotation based wiring
<?php
class MySampleService implements IMySampleService {
private $sampleDao;
/**
* @Inject
* @Named('TheSampleDao')
*/
public function __construct(ISampleDao $sampleDao)
{
$this->sampleDao = $sampleDao;
}
}

35. Real World Dependency Injection
External configuration - XML
<?xml version="1.0" encoding="UTF-8" ?>
<beans>
<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>

36. Real World Dependency Injection
External configuration - YAML
services:
SampleDao:
class: SampleDao
arguments: ['app_sample', 'iSampleId', 'BoSample']
SampleService:
class: SampleService
arguments: [@SampleDao]

37. Real World Dependency Injection
External configuration - PHP
<?php
class BeanCache extends Beanfactory_Container_PHP {
protected function createSampleDao() {
$oBean = new SampleDao('app_sample',
'iSampleId', 'BoSample');
return $oBean;
}
protected function createMySampleService() {
$oBean = new MySampleService(
$this->getBean('SampleDao')
);
return $oBean;
}
}

38. Real World Dependency Injection
Ready to unlock the door?

39. Real World Dependency Injection
Unittesting made easy

40. Real World Dependency Injection
Unittesting made easy
<?php
require_once 'PHPUnit/Framework.php';
class ServiceTest extends PHPUnit_Framework_TestCase {
public function testSampleService() {
// set up dependencies
$sampleDao = $this->getMock('ISampleDao');
$service = new MySampleService($sampleDao);
// run test case
$return = $service->doWork();
// check assertions
$this->assertTrue($return);
}
}

41. Real World Dependency Injection
One class, multiple configurations

42. Real World Dependency Injection
One class, multiple configurations
Page Exporter
Page Exporter
Released / /Published
Released Published Workingcopy
Workingcopy
Pages
Pages Pages
Pages

43. Real World Dependency Injection
One class, multiple configurations
<?php
abstract class PageExporter {
protected function setPageDao(IPageDao $pageDao) {
$this->pageDao = $pageDao;
}
}

44. Real World Dependency Injection
One class, multiple configurations
<?php
abstract class PageExporter {
protected function setPageDao(IPageDao $pageDao) {
$this->pageDao = $pageDao;
}
}
Remember:
The contract!

45. Real World Dependency Injection
One class, multiple configurations
<?php
class PublishedPageExporter extends PageExporter {
public function __construct() {
$this->setPageDao(new PublishedPageDao());
}
}
class WorkingCopyPageExporter extends PageExporter {
public function __construct() {
$this->setPageDao(new WorkingCopyPageDao());
}
}

46. Real World Dependency Injection
One class, multiple configurations
"Only deleted code is good code!"
Oliver Gierke

47. Real World Dependency Injection
One class, multiple configurations
<?php
class PageExporter {
public function __construct(IPageDao $pageDao) {
$this->pageDao = $pageDao;
}
}

48. Real World Dependency Injection
One class, multiple configurations
<?xml version="1.0" encoding="UTF-8" ?>
<beans>
<bean id="ExportLive" class="PageExporter">
<constructor-arg ref="PublishedPageDao" />
</bean>
<bean id="ExportWorking" class="PageExporter">
<constructor-arg ref="WorkingCopyPageDao" />
</bean>
</beans>

49. Real World Dependency Injection
One class, multiple configurations
<?php
// create ApplicationContext instance
$ctx = new ApplicationContext();
// retrieve live exporter
$exporter = $ctx->getBean('ExportLive');
// retrieve working copy exporter
$exporter = $ctx->getBean('ExportWorking');

50. Real World Dependency Injection
One class, multiple configurations II

51. Real World Dependency Injection
One class, multiple configurations II
http://editor.loc/page/[id]/headline/
http://editor.loc/page/[id]/content/
http://editor.loc/page/[id]/teaser/

52. Real World Dependency Injection
One class, multiple configurations II
<?php
class EditPart extends Mvc_Action_AFormAction {
private $pagePartsManager;
private $type;
public function __construct(IPagePartsManager $pm) {
$this->pagePartsManager = $pm;
}
public function setType($ptype) {
$this->type = (int) $type;
}
protected function process(Bo_ABo $formBackObj) {
}
}

53. Real World Dependency Injection
One class, multiple configurations II
<?xml version="1.0" encoding="UTF-8" ?>
<beans>
<bean id="EditHeadline" class="EditPart">
<constructor-arg ref="PagePartDao" />
<property name="Type" const="PType::Headline" />
</bean>
<bean id="EditContent" class="EditPart">
<constructor-arg ref="PagePartDao" />
<property name="Type" const="PType::Content" />
</bean>
</beans>

54. Real World Dependency Injection
Mocking external service access

55. Real World Dependency Injection
Mocking external service access
WS-
WS-
Booking service
Booking service Webservice
Webservice
Connector
Connector

56. Real World Dependency Injection
Mocking external service access
WS-
WS-
Booking service
Booking service Webservice
Webservice
Connector
Connector
Remember:
The contract!

57. Real World Dependency Injection
Mocking external service access
FS-
FS-
Booking service
Booking service Filesystem
Filesystem
Connector
Connector

58. Real World Dependency Injection
Mocking external service access
FS-
FS-
Booking service
Booking service Filesystem
Filesystem
Connector
Connector
fullfills the
contract!

59. Real World Dependency Injection
Clean, readable code

60. Real World Dependency Injection
Clean, readable code
<?php
class DeletePage extends Mvc_Action_AAction {
private $pageManager;
public function __construct(IPageManager $pm) {
$this->pageManager = $pm;
}
protected function execute(Mvc_Request $request) {
$this->pageManager->delete(
(int) $request->get('pageId'));
return new ModelAndView($this->getSuccessView());
}
}

61. Real World Dependency Injection
No framework dependency

62. Real World Dependency Injection
No framework dependency
<?php
class MySampleService implements IMySampleService {
private $sampleDao;
public function __construct(ISampleDao $sampleDao) {
$this->sampleDao = $sampleDao;
}
public function getSample($sampleId) {
try {
return $this->sampleDao->readById($sampleId);
}
catch(DaoException $exception) {}
}
}

63. Real World Dependency Injection
Benefits
Loose coupling, reuse of components!

64. Real World Dependency Injection
Benefits
Can reduce the amount of code!

65. Real World Dependency Injection
Benefits
Helps developers to
understand the code!

66. Real World Dependency Injection
Cons – No JSR330 for PHP
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, …

67. Real World Dependency Injection
Cons – Developers need mindshift
Configuration ↔ Runtime

68. http://joind.in/3002

69. Image Credits
http://www.sxc.hu/photo/1028452