The document discusses using inversion of control (IoC) and dependency injection (DI) to decouple classes and make them more flexible and testable in PHP. It provides an example of refactoring an authenticator class to depend on a user repository interface rather than a concrete class. This decreases coupling and allows different repositories to be injected. It then discusses using a service container to further abstract object creation and injection of dependencies defined through code or configuration.

1. IoC with PHP
Chris Weldon
Dallas TechFest 2011

2. Before We Begin
http://bit.ly/rf1pxR
git://github.com/neraath/ioc-php-talk.git

3. Your Guide: Chris Weldon
• Fightin’ Texas Aggie
• .Net and PHP Developer
• UNIX and Windows Sysadmin
• Senior Consultant at Improving Enterprises
• Contact Me: chris@chrisweldon.net

4. Agile, Microsoft, Open Technologies, UX
Applied Training, Coaching, Mentoring
Certified Consulting
Rural Sourcing
Recruiting Services

5. Before We Get to IoC...
<?php
class Authenticator {
private $_repository;
public function __construct() {
$this->_repository = new DataAccessLayer();
}
public function authenticate($username, $password) {
$hashedPassword = md5($password);
$user = $this->_repository->findByUsernameAndPassword(
$username, $hashedPassword);
return $user === null;
}
}

6. What are the problems?

7. What are the problems?
• Strongly coupled to DataAccessLayer

8. What are the problems?
• Strongly coupled to DataAccessLayer
Authenticator
authenticate() : bool
DataAccessLayer
findByUsernameAndPassword : array

9. What are the problems?
• Strongly coupled to DataAccessLayer
•
Authenticator
Very inflexible authenticate() : bool
DataAccessLayer
findByUsernameAndPassword : array

10. What are the problems?
• Strongly coupled to DataAccessLayer
•
Authenticator
Very inflexible authenticate() : bool
• How to configure DataAccessLayer?
DataAccessLayer
findByUsernameAndPassword : array

11. What are the problems?
• Strongly coupled to DataAccessLayer
•
Authenticator
Very inflexible authenticate() : bool
• How to configure DataAccessLayer?
•
DataAccessLayer
Let it read configs? findByUsernameAndPassword : array

12. What are the problems?
• Strongly coupled to DataAccessLayer
•
Authenticator
Very inflexible authenticate() : bool
• How to configure DataAccessLayer?
•
DataAccessLayer
Let it read configs? findByUsernameAndPassword : array
• How to test the Authenticator?

13. Let’s solve it
• What are our goals?
• Decrease coupling
• Increase configurability

14. <?php
interface IUserRepository {
function findByUsernameAndPassword($username, $password);
}
class DataAccessLayer implements IUserRepository {
private $_configParams;
private $_database;
public function __construct(array $configParams) {
$this->_configParams = $configParams;
$this->_database = Zend_Db::factory('Pdo_Mysql', $this->_configParams);
}
public function findByUsernameAndPassword($username, $password) {
$query = 'SELECT * FROM users WHERE username = ? AND password = ?';
$result = $this->_database->fetchAll($query, $username, $password);
return $result;
}
}

15. Our Updated Authenticator
<?php
class Authenticator {
private $_repository;
public function __construct(IUserRepository $repository) {
$this->_repository = $repository;
}
public function authenticate($username, $password) {
$hashedPassword = md5($password);
$user = $this->_repository->findByUsernameAndPassword(
$username, $hashedPassword);
return $user === null;
}
}

16. Time to Consume
<?php
class LoginController {
public function login($username, $password) {
$configuration = Zend_Registry::get('dbconfig');
$dal = new DataAccessLayer($configuration);
$authenticator = new Authenticator($dal);
if ($authenticator->authenticate($username, $password)) {
// Do something to log the user in.
}
}
}

17. Goal Recap
• What were our goals?
• Decrease coupling
• Increase configurability

18. Goal Recap
• What were our goals?
• Decrease coupling
• Increase configurability

19. Goal Recap
• What were our goals?
• Decrease coupling
• Increase configurability

20. What You Saw Was IoC
• Inversion of Control changes direction of responsibility
• Someone else responsible for creating and providing my
dependencies
• Most commonly applied pattern: Dependency Injection
• Follows Dependency Inversion Principle from SOLID
• Culture War: IoC vs. DI vs. Naming vs. Principles vs. Ideology

21. Dependency Inversion
• “High-level modules should not depend upon low level modules. They
should depend upon abstractions.
• “Abstractions should not depend upon details. Details should depend
upon abstractions.”
Robert Martin

22. Let’s Draw

23. Let’s Draw
Authenticator
authenticate() : bool
DataAccessLayer
findByUsernameAndPassword : array

24. Let’s Draw
Authenticator
authenticate() : bool
DataAccessLayer
findByUsernameAndPassword : array

25. Let’s Draw
Authenticator
authenticate() : bool
Authenticator
authenticate() : bool
IUserRepository
findByUsernameAndPassword : array
DataAccessLayer
findByUsernameAndPassword : array
DataAccessLayer
findByUsernameAndPassword : array

26. Benefit: Flexibility
<?php
class WebServiceUserRepository implements IUserRepository {
public function findByUsernameAndPassword($username, $password) {
// Fetch our user through JSON or SOAP
}
}
class OAuthRepository implements IUserRepository {
public function findByUsernameAndPassword($username, $password) {
// Connect to your favorite OAuth provider
}
}

27. Benefit: Testable
<?php
class WhenAuthenticating extends PHPUnit_Framework_TestCase {
public function testGivenInvalidUsernameAndPasswordShouldReturnFalse() {
$stub = $this->getMock('IUserRepository');
$stub->expects($this->any())
->method('findByUsernameAndPassword')
->will($this->returnValue(null));
$authenticator = new Authenticator($stub);
$this->assertFalse($authenticator->authenticate('user', 'pass'));
}
}

28. Dependency Injection
• Now we can inject our dependencies to our consumer classes
• Still requires some other class to be tightly coupled to both of those
• Need a container that can help abstract the relationship between the
interface and implementation

29. <?php
class UserRepositoryContainer {
/** @return IUserRepository **/
public function getRepository() {
$container = new DataAccessLayer(array(
'dsn' => 'mysql://localhost/database',
'username' => 'user',
'password' => 'pass'
));
return $container;
}
}
class LoginController {
public function login($username, $password) {
$container = new UserRepositoryContainer();
$repository = $container->getRepository();
$authenticator = new Authenticator($repository);
// ...
}
}

30. Container Woes
• No uniform interface by which to access services
• Still tightly coupled with dependencies
• Configurability of the container difficult
• How to auto-inject dependency for configured consumer classes?

31. Symfony Dependency Injection
Container
• Two Ways to Setup and Use sfServiceContainer
• Create subclass
• Manual registration via code or config

32. sfServiceContainer Subclass
<?php
class UserRepositoryContainer extends sfServiceContainer {
protected function getUserRepositoryService() {
$container = new DataAccessLayer($this['repository.config']);
return $container;
}
}

33. Consuming the Container
<?php
class LoginController {
public function login($username, $password) {
$configuration = Zend_Registry::get('dbconfig');
$container = new UserRepositoryContainer(array(
'repository.config' => $configuration
));
$repository = $container->userRepository;
$authenticator = new Authenticator($repository);
if ($authenticator->authenticate($username, $password)) {
// Do something to log the user in.
}
}
}

34. That’s Pretty Nice
• Configurability a lot easier
• Uniform interface for accessing services
• How does this scale when there are lots of dependencies?
• Aren’t we still coupling the container to the implementation at
compile time?

35. The Builder
• Provides a uniform way of describing services, without custom
containers
• For each service description, we have the flexibility to configure an
object:
• At instantiation (Constructor Injection)
• Post-instantiation (Setter/Method Injection)

36. How to Describe a Service
• Code-based or Config-based
• Code-based allows for run-time changing of injection parameters
• Config-based provides a way to change parameters between
environments with no code changes
• Not mutually exclusive

37. Code-Based Description
<?php
// Imagine this is a bootstrap file.
$configuration = Zend_Registry::get('dbconfig');
$builder = new sfServiceContainerBuilder();
$builder->register('user_repository', 'DataAccessLayer')
->addArgument($configuration)
// OR ->addArgument('%repository.config%') from earlier
->setShared(false);
$builder->register('authenticator', 'Authenticator')
->addArgument(new sfServiceReference('user_repository'));
Zend_Registry::set('di_container', $builder);

38. Config-Based Description
<?xml version="1.0" ?>
<container xmlns="http://symfony-project.org/2.0/container">
<parameters>
<parameter key="user_repository.dsn">mysql://localhost/database</parameter>
<parameter key="user_repository.username">username</parameter>
<parameter key="user_repository.password">password</parameter>
</parameters>
<services>
<service id="user_repository" class="DataAccessLayer" shared="false">
<argument type="collection">
<argument key="dsn">%user_repository.dsn%</argument>
<argument key="username">%user_repository.username%</argument>
<argument key="password">%user_repository.password%</argument>
</argument>
</service>
<service id="authenticator" class="Authenticator">
<argument type="service" id="user_repository" />
</service>
</services>
</container>

39. Loading the Config
<?php
// Imagine this is a bootstrap file.
$builder = new sfServiceContainerBuilder();
$loader = new sfServiceContainerLoaderFileXml($builder);
$loader->load('/pathTo/services.xml');
Zend_Registry::set('di_container', $builder);

40. Using the Container
<?php
class LoginController {
public function login($username, $password) {
$container = Zend_Registry::get('di_container');
$authenticator = $container->authenticator;
if ($authenticator->authenticate($username, $password)) {
// Do something to log the user in.
}
}
}

41. High Level Picture
DataAccessLayer
findByUsernameAndPassword : array
IUserRepository
findByUsernameAndPassword : array
sfServiceContainerBuilder
getService : object
setService : void
hasService : bool
Authenticator
authenticate() : bool
IAuthenticator
authenticate() : bool
sfServiceContainerInterface
getService : object
LoginController setService : void
login() : void hasService : bool

42. When to Use a DI Container

43. When to Use a DI Container
• Not for model objects (e.g. Orders, Documents, etc.)

44. When to Use a DI Container
• Not for model objects (e.g. Orders, Documents, etc.)
• Great for resource requirements (e.g. repositories, loggers, etc.)

45. When to Use a DI Container
• Not for model objects (e.g. Orders, Documents, etc.)
• Great for resource requirements (e.g. repositories, loggers, etc.)
• Really great for plugin-type architecture

46. When to Use a DI Container
• Not for model objects (e.g. Orders, Documents, etc.)
• Great for resource requirements (e.g. repositories, loggers, etc.)
• Really great for plugin-type architecture
• But not necessary to use Dependency Injection!

47. Other Considerations

48. Other Considerations
• Learning curve

49. Other Considerations
• Learning curve
• Tracking dependencies

50. Other Considerations
• Learning curve
• Tracking dependencies
• Dependency changes

51. Other Considerations
• Learning curve
• Tracking dependencies
• Dependency changes
• Setter/method vs. constructor injection

52. Service Lifetimes
• setShared() allows you to specify context persistence
• If shared, acts like a singleton
• Useful if construction is expensive or state persistence required

53. Let’s Code

54. Thank You!
http://bit.ly/rf1pxR
git://github.com/neraath/ioc-php-talk.git