deSymfonyDay
Barcelona 2014
DIC To The
Limit
Ronny López
ABOUT ME US
Hard way learner	

!
Technical Lead at Social Point	

Do stuff atTangoTree in the nights	

!
@ronn...
AGENDA
• The problems	

• Dependency Injection	

• Coupling done right	

• Dependency Inversion Principle	

• Types of DI	...
THE PROBLEMS
• We require to switch out data access layer without
compromising all the other parts of the application	

• ...
YAGNI	

You aren't gonna need it, let’s go home!
IN CASEYOU NEED IT
• You have to do Dependency Injection, correctly	

• You have to know and apply Dependency Inversion
Pr...
WHAT WE REALLY WANT IS
• Code that is easy to test	

• Clear separation of infrastructure logic from
application logic	

•...
WHY?
• Multiple deployments share parts of the same code,
but each deployment has specific infrastructure
needs	

• Multipl...
“The only way to
go fast, is to go
well”

Uncle Bob
DEPENDENCY 	

INJECTION
Dependency injection is a
simple way to decouple
classes from what they
depend on
Dependency injection
decouples classes
construction from the
construction of it’s
dependencies
IS IT ALL ABOUT
COUPLING?
COUPLING
Mod A Mod B
Mod C Mod D
Tight (high, strong)
Mod A Mod B
Mod C Mod D
Loose (low, weak)
Mod A Mod B
Mod C Mod D
No...
COUPLING
• The history of software shows that coupling is bad,
but it also suggest that coupling is unavoidable 	

• An ab...
COUPLING DONE RIGHT
• Components make no assumptions about what other
components do, but rely on their contracts	

• Use a...
DEPENDENCY INVERSION
PRINCIPLE
High-level modules should
not depend on low-level
modules. 	

Both should depend on
abstractions
Abstractions should not
depend on details. 	

Details should depend on
abstractions
DEPENDENCY INVERSION
• Decouple high level parts of the system from low level
parts by using interfaces
OrderProcessor OrderRepository
MySqlOrderRepository
CassandraOrderRepository
LockSystem
RedisLockSystem
ZooKeeperLockSyste...
TYPES OF DEPENDENCY
INJECTIONS	

!
TYPES OF DI
• Constructor Injection	

• Setter Injection	

• Interface Injection	

• Property Injection	

• Service Locator
CONSTRUCTOR INJECTION
• Injects the dependencies via constructor	

• It ensures that the choice of dependency is immutable...
CONSTRUCTOR INJECTION
• It ensures that the choice of
dependency is immutable	

• The constructor is only ever
called once...
CONSTRUCTOR INJECTION
• Try to always use constructor injection	

• If dealing with legacy code that does not support it,
...
SETTER INJECTION
• Inject the dependencies via a setter method	

• The “injector” has to call the method in order to injec...
SETTER INJECTION
• Works “well” with optional
dependencies



If you do not need the
dependency, then just do not
call the...
SETTER INJECTION
TIPS
• Avoid setter injections (the choice of dependencies
is not inmutable)	

• If you do Dependency Inv...
SETTER INJECTION
EXAMPLE
use PsrLogLoggerInterface;!
!
final class OrderProcessor!
{!
private $logger;!
!
function __const...
INTERFACE INJECTION
• Define and use interfaces for the injection	

• Allows certain objects to be injected into other obje...
PROPERTY INJECTION
• Allows setting public fields of the class directly	

• There are mainly only disadvantages to using pr...
PROPERTY INJECTION
• Useful if you are working with
code that is out of your control,
such as in a 3rd party library,
whic...
SERVICES LOCATOR
• Is an object that knows how to get all of the services that an
another service might need
interface Com...
SERVICE LOCATOR
• It’s easy to use and abuse due
to its straightforward behaviour	

• Not all use cases are bad, for
examp...
SERVICE LOCATOR
TIPS
• Use a segregated interface for the locator, do not
depends on the whole locator (container)	

!
• L...
DEPENDENCY INJECTION 	

CONTAINER
Dependency Injection
Container is simply an
object that manages the
instantiation of other objects
Automagically creates a
given type with all the
required dependencies
DIC
• Most of the time you do not need a DIC to benefit from
Dependency Injection	

• But… creating and maintaining the dep...
DEPENDENCY INJECTION 	

CONTAINERS IN PHP
PHP DIC IMPLEMENTATIONS
• Twittee 	

• Pimple	

• IlluminateDi	

• ZendDi	

• SymfonyDependencyInjection	

• http://php-di...
SYMFONY 

DEPENDENCY
INJECTION CONTAINER
The Dependency Injection
component allows you to
standardize and centralize
the way objects are
constructed in a SF
applic...
HOW IT WORKS?
• Reads definition of how objects (services) should be
constructed (XML,YAML, PHP, etc…)	

• Collects all defi...
ADVANCED
HOW IT WORKS
• Compiler Passes	

• Container Extensions	

• Services Configurator	

• Tagged Services
SYMFONY DIC
• Basic (and advances) usages are well documented in
the Symfony official documentation	

• Probably you are co...
INTERCHANGEABLE
SERVICES
OrderProcessor OrderRepository
MySqlOrderRepository
CassandraOrderRepository
LockSystem
RedisLockSystem
ZooKeeperLockSyste...
final class OrderProcessor!
{!
private $orderRepository;!
private $lockSystem;!
private $objectStore;!
!
function __constr...
services:!
! order_processor:!
! ! class: OrderProcessor!
arguments:!
! ! ! object_store: @object_store!
! ! ! order_repos...
THE PROBLEM
• It’s not possible to decide in advance what concrete
implementation a deployment or environment is going
to ...
SERVICES SETUP
Deployment Environment Concrete Implementation
DRAGON TESTING in-memory
DRAGON STAGING/QA redis
DRAGON PROD...
SOLUTIONS
1. Loading different configurations depending on the
environment and aliasing services	

2. Using synthetic servi...
1- LOADING DIFFERENT CONFIGURATIONS
Load different configurations depending on the
kernel.environment
• Probably easy to se...
!
namespace AcmeDemoBundleDependencyInjection;!
!
use SymfonyComponentDependencyInjectionContainerBuilder;!
use SymfonyCom...
2- USING SYNTHETIC SERVICES AND ALIAS
Define abstraction as “synthetic” services
• Probably easy to setup for
testing/dummy...
!
namespace AcmeDemoBundleDependencyInjection;!
!
use SymfonyComponentDependencyInjectionContainerBuilder;!
use SymfonyCom...
3- MANAGING SEMANTIC CONFIGURATIONS
WITH EXTENSIONS
• Instead of having the user override individual
parameters, you let t...
3- MANAGING SEMANTIC CONFIGURATIONS
WITH EXTENSIONS
• Good fit if you are building a bundle to be used by 3rd
parties and y...
class Configuration implements ConfigurationInterface!
{!
protected function addObjectStoreSection(ArrayNodeDefinition $ro...
3- MANAGING SEMANTIC CONFIGURATIONS
WITH EXTENSIONS
• More powerful than simply
defining parameters: a specific
option value...
4- USING A CUSTOM INJECTOR
• Let’s forget the Symfony DIC for a moment	

• Let’s go back to dependency management problem
...
services:!
! order_processor:!
! ! class: OrderProcessor!
arguments:!
! ! ! object_store: @object_store!
! ! ! order_repos...
“A good architecture allows
you to defer critical decisions,
it doesn’t force you to defer
them. 	

However, if you can de...
“A good architecture allows
volatile decisions to be easily
changed”	

!
Uncle Bob
services:!
! order_processor:!
! ! class: OrderProcessor!
arguments:!
! ! ! object_store: @object_store!
! ! ! order_repos...
Core Framework
Payment Component
Analytics Component
Object Store Lock System
Component Exports Depends On
Unit Of Work St...
Core Component Object Store Lock System
Component Exports Depends On
Unit Of Work Storage Driver
Implementations
Redis, Zo...
Payment Component Order Processor Product Repository
Order Repository
Config, API
MySql, C*
namespace SPCoreGamePayment;!
!...
WHERE DOESTHE MAGIC COME FROM?
• There is not such “magic”	

• Each component define it’s dependencies in a easy and
legibl...
HOW?
• First, collect services definitions from installed
components	

• Second, inject services definitions into the Symfon...
USING SYMFONY
• Collect services definitions from installed components	

• Inject services definitions into the Symfony (or ...
use SymfonyComponentDependencyInjection as DI;!
!
!
final class ComponentDependencyInjector implements DICompilerCompilerP...
use SymfonyComponentHttpKernelKernel;!
use SymfonyComponentConfigLoaderLoaderInterface;!
!
class AppKernel extends Kernel!...
namespace SPCoreBundleGameFrameworkBundle;!
!
use SymfonyComponentDependencyInjectionCompilerPassConfig;!
use SymfonyCompo...
[SPCoreBridgeSymfonyDependencyInjectionExceptionServiceNotFoundException]
Component "core.game.framework" requires the ser...
services:!
!
! core.game.framework.lock_system:!
! ! public: false!
! ! class: SPCoreComponentLockRedisLockSystem!
! ! arg...
4- USING A CUSTOM INJECTOR
• Complete control of
component dependencies	

• Very limited in features (only
constructor inj...
CONCLUSIONS
• You have the tools, use the best tool that solve your
problems	

• Don’t be afraid of going to the limit wit...
SOME REFERENCES
http://www.objectmentor.com/resources/articles/dip.pdf
!
http://www.martinfowler.com/articles/injection.ht...
THANK YOU
For your attention
@ronnylt
DIC To The Limit – deSymfonyDay, Barcelona 2014
DIC To The Limit – deSymfonyDay, Barcelona 2014
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Applying Dependency Inversion and Dependency Injections principles correctly in Symfony

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DIC To The Limit – deSymfonyDay, Barcelona 2014

  1. 1. deSymfonyDay Barcelona 2014 DIC To The Limit
  2. 2. Ronny López ABOUT ME US Hard way learner ! Technical Lead at Social Point Do stuff atTangoTree in the nights ! @ronnylt
 www.tangotree.io
 https://github.com/ronnylt
  3. 3. AGENDA • The problems • Dependency Injection • Coupling done right • Dependency Inversion Principle • Types of DI • Dependency Injection Containers • Symfony Dependency Injection Container • Interchangeable Services
  4. 4. THE PROBLEMS • We require to switch out data access layer without compromising all the other parts of the application • We need to use different implementations in different deployments (dragon game, monster game, etc…) • We wish to deploy the application in different environments (testing, integration, staging, production, etc…) • We need different configurations in each environment
  5. 5. YAGNI You aren't gonna need it, let’s go home!
  6. 6. IN CASEYOU NEED IT • You have to do Dependency Injection, correctly • You have to know and apply Dependency Inversion Principles
  7. 7. WHAT WE REALLY WANT IS • Code that is easy to test • Clear separation of infrastructure logic from application logic • Interchangeable infrastructure
  8. 8. WHY? • Multiple deployments share parts of the same code, but each deployment has specific infrastructure needs • Multiple environments with different needs • We want to automatically test all the things • We want to go fast, and the only way to go fast is… you know…
  9. 9. “The only way to go fast, is to go well”
 Uncle Bob
  10. 10. DEPENDENCY INJECTION
  11. 11. Dependency injection is a simple way to decouple classes from what they depend on
  12. 12. Dependency injection decouples classes construction from the construction of it’s dependencies
  13. 13. IS IT ALL ABOUT COUPLING?
  14. 14. COUPLING Mod A Mod B Mod C Mod D Tight (high, strong) Mod A Mod B Mod C Mod D Loose (low, weak) Mod A Mod B Mod C Mod D None Coupling is a measure of the independency of components/modules
  15. 15. COUPLING • The history of software shows that coupling is bad, but it also suggest that coupling is unavoidable • An absolutely decoupled application is useless because it adds no value • Developers can only add value by coupling things together
  16. 16. COUPLING DONE RIGHT • Components make no assumptions about what other components do, but rely on their contracts • Use an interface to define a type and focus on what is important • Concrete implementations of the interfaces should be be instantiated outside the component
  17. 17. DEPENDENCY INVERSION PRINCIPLE
  18. 18. High-level modules should not depend on low-level modules. Both should depend on abstractions
  19. 19. Abstractions should not depend on details. Details should depend on abstractions
  20. 20. DEPENDENCY INVERSION • Decouple high level parts of the system from low level parts by using interfaces
  21. 21. OrderProcessor OrderRepository MySqlOrderRepository CassandraOrderRepository LockSystem RedisLockSystem ZooKeeperLockSystem <<interface>> <<interface>> ObjectStore RedisStorageDriver InMemoryStorageDriver RiakStorageDriver StorageDriver <<interface>>
  22. 22. TYPES OF DEPENDENCY INJECTIONS !
  23. 23. TYPES OF DI • Constructor Injection • Setter Injection • Interface Injection • Property Injection • Service Locator
  24. 24. CONSTRUCTOR INJECTION • Injects the dependencies via constructor • It ensures that the choice of dependency is immutable ! class EnergyBuyCommandHandler implements CommandHandler! {! private $playerRepository;! ! private $configRepository;! ! public function __construct(! ! ! PlayerRepository $playerRepository, ! ! ! ConfigRepository $config! ! )! {! $this->playerRepository = $playerRepository;! $this->configRepository = $config;! }! }!
  25. 25. CONSTRUCTOR INJECTION • It ensures that the choice of dependency is immutable • The constructor is only ever called once when the object is created, so you can be sure that the dependency will not change during the object's lifetime Pros Cons • It is not suitable for working with optional dependencies • Difficult to use in combination with class hierarchies
  26. 26. CONSTRUCTOR INJECTION • Try to always use constructor injection • If dealing with legacy code that does not support it, consider using an adapter class with constructor injection • Depends on abstractions (interfaces), not concrete implementations TIPS
  27. 27. SETTER INJECTION • Inject the dependencies via a setter method • The “injector” has to call the method in order to inject the dependency ! class LoggerChain implements SQLLogger! {! private $loggers = array();! ! public function setLogger(SQLLogger $logger)! {! $this->logger = $logger;! }! }!
  28. 28. SETTER INJECTION • Works “well” with optional dependencies
 
 If you do not need the dependency, then just do not call the setter • You can call the setter multiple times.
 
 This is particularly useful if the method adds the dependency to a collection Pros Cons • Works “well” with optional dependencies 
 
 Are you sure you need optional dependencies? • You can call the setter multiple times • You are not sure if the dependency was set
  29. 29. SETTER INJECTION TIPS • Avoid setter injections (the choice of dependencies is not inmutable) • If you do Dependency Inversion right, probably YANGI • Remember, your classes depend on abstractions, not concrete implementations, so you can use Null or Dummy implementations when necessary
  30. 30. SETTER INJECTION EXAMPLE use PsrLogLoggerInterface;! ! final class OrderProcessor! {! private $logger;! ! function __construct(. . ., LoggerInterface $logger)! {! $this->logger = $logger;! }! }! ! final class GoodManLogger implements LoggerInterface {…}! ! final class LogstarLogger implements LoggerInterface {…}! ! final class NullLogger implements LoggerInterface {…}! Instead of having a setter method to inject the logger, use constructor injection and use the appropriate logger implementation in each case
  31. 31. INTERFACE INJECTION • Define and use interfaces for the injection • Allows certain objects to be injected into other objects, that implement a common interface • It’s a kind of setter injection, so same pros and cons interface ContainerAwareInterface! {! public function setContainer(ContainerInterface $container = null);! }! ! class ContainerAwareEventDispatcher implements ContainerAwareInterface! {! public function setContainer(ContainerInterface $container = null)! {! }! }!
  32. 32. PROPERTY INJECTION • Allows setting public fields of the class directly • There are mainly only disadvantages to using property injection, it is similar to setter injection but with additional important problems ! ! class NewsletterManager! {! public $mailer;! ! // ...! }!
  33. 33. PROPERTY INJECTION • Useful if you are working with code that is out of your control, such as in a 3rd party library, which uses public properties for its dependencies Pros Cons • You cannot control when the dependency is set at all, it can be changed at any point in the object's lifetime • You cannot use type hinting so you cannot be sure what dependency is injected except by writing into the class code to explicitly test the class instance before using it
  34. 34. SERVICES LOCATOR • Is an object that knows how to get all of the services that an another service might need interface CommandHandlerLocator ! {! public function locate($commandName);! }! ! ! class ContainerCommandHandlerLocator implements CommandHandlerLocator! {! private $container;! ! public function __construct(ContainerInterface $container)! {! $this->container = $container;! }! ! public function locate($commandName)! {! if (!$this->container->has($commandName)) {! throw new NotFoundException('Unable to find command handler');! }! ! return $this->container->get($commandName);! }! }!
  35. 35. SERVICE LOCATOR • It’s easy to use and abuse due to its straightforward behaviour • Not all use cases are bad, for example when you want to load services on demand at runtime Pros Cons • It hides dependencies in your code making them difficult to figure out and potentially leads to errors that only manifest themselves at runtime • It becomes unclear what are the dependencies of a given class • It’s easy to abuse • It’s consider and anti-pattern (but there are valid use cases for it)
  36. 36. SERVICE LOCATOR TIPS • Use a segregated interface for the locator, do not depends on the whole locator (container) ! • Limit the types of services a locator provides
  37. 37. DEPENDENCY INJECTION CONTAINER
  38. 38. Dependency Injection Container is simply an object that manages the instantiation of other objects
  39. 39. Automagically creates a given type with all the required dependencies
  40. 40. DIC • Most of the time you do not need a DIC to benefit from Dependency Injection • But… creating and maintaining the dependencies by hand can become a nightmare pretty fast • A DIC manages objects from their instantiation to their configuration • The objects themselves should not know that they are managed by a container and should not know nothing about it
  41. 41. DEPENDENCY INJECTION CONTAINERS IN PHP
  42. 42. PHP DIC IMPLEMENTATIONS • Twittee • Pimple • IlluminateDi • ZendDi • SymfonyDependencyInjection • http://php-di.org/ • Build your own
  43. 43. SYMFONY 
 DEPENDENCY INJECTION CONTAINER
  44. 44. The Dependency Injection component allows you to standardize and centralize the way objects are constructed in a SF application
  45. 45. HOW IT WORKS? • Reads definition of how objects (services) should be constructed (XML,YAML, PHP, etc…) • Collects all definitions and builds a container • When requested, creates objects and injects the dependencies
  46. 46. ADVANCED HOW IT WORKS • Compiler Passes • Container Extensions • Services Configurator • Tagged Services
  47. 47. SYMFONY DIC • Basic (and advances) usages are well documented in the Symfony official documentation • Probably you are comfortable creating your own objects via the container • So, let’s try to solve the problems we stated at the beginning
  48. 48. INTERCHANGEABLE SERVICES
  49. 49. OrderProcessor OrderRepository MySqlOrderRepository CassandraOrderRepository LockSystem RedisLockSystem ZooKeeperLockSystem <<interface>> <<interface>> ObjectStore RedisStorageDriver InMemoryStorageDriver RiakStorageDriver StorageDriver <<interface>>
  50. 50. final class OrderProcessor! {! private $orderRepository;! private $lockSystem;! private $objectStore;! ! function __construct(! ! ! OrderRepository $repository, ! ! ! LockSystem $lockSystem, ! ! ! ObjectStore $objectStore)! {! $this->orderRepository = $repository;! $this->lockSystem = $lockSystem;! $this->objectStore = $objectStore;! }! }! ! final class ObjectStore! {! function __construct(StorageDriver $driver)! {! }! }! ! ! interface StorageDriver ! {}! ! final class RiakStorageDriver implements StorageDriver! {}! ! final class RedisStorageDriver implements StorageDriver! {}! ! final class InMemoryStorageDriver implements StorageDriver! {}! ! interface LockSystem ! {}! ! final class RedisLockSystem implements LockSystem! {}! ! final class ZooKeeperLockSystem implements LockSystem! {}! interface OrderRepository {}! ! final class MySqlOrderRepository implements OrderRepository! {}! ! final class CassandralOrderRepository implements OrderRepository! {}!
  51. 51. services:! ! order_processor:! ! ! class: OrderProcessor! arguments:! ! ! ! object_store: @object_store! ! ! ! order_repository: [mysql|cassandra] ! ! ! ! lock_system: [redis|zookeeper]! ! ! ! ! ! ! object_store:! ! ! class: ObjectStore! ! ! arguments:! ! ! storage_driver: [riak|redis|inmemory]! MySqlOrderRepository CassandraOrderRepository RedisLockSystem ZooKeeperLockSystem RedisStorageDriver InMemoryStorageDriver RiakStorageDriver
  52. 52. THE PROBLEM • It’s not possible to decide in advance what concrete implementation a deployment or environment is going to use • We must configure dependencies for all the concrete implementations and each one has their own dependencies
  53. 53. SERVICES SETUP Deployment Environment Concrete Implementation DRAGON TESTING in-memory DRAGON STAGING/QA redis DRAGON PROD mysql MONSTER TESTING in-memory MONSTER PROD cassandra
  54. 54. SOLUTIONS 1. Loading different configurations depending on the environment and aliasing services 2. Using synthetic services and aliases 3. Managing semantic configuration with extensions 4. Using a custom injector
  55. 55. 1- LOADING DIFFERENT CONFIGURATIONS Load different configurations depending on the kernel.environment • Probably easy to setup for testing/dummy services Pros Cons • The choice is coupled to the environment • All services get defined, even when you are not going to use them
  56. 56. ! namespace AcmeDemoBundleDependencyInjection;! ! use SymfonyComponentDependencyInjectionContainerBuilder;! use SymfonyComponentDependencyInjectionLoaderXmlFileLoader;! use SymfonyComponentHttpKernelDependencyInjectionExtension;! use SymfonyComponentConfigFileLocator;! ! class AcmeDemoExtension extends Extension! {! public function load(array $configs, ContainerBuilder $container)! {! $loader = new YamlFileLoader($container, new FileLocator(__DIR__.'/../Resources/config'));! $loader->load('services.yml');! ! if ($this->container->getParameter('kernel.environment') == 'test') {! $loader->load('services_test.yml');! }! }! ! public function getAlias()! {! return 'acme_demo';! }! }! services:! storage_driver:! alias: storage_driver.riak! ! storage_driver.riak:! class: RiakStorageDriver! ! storage_driver.redis:! class: RedisStorageDriver! ! storage_driver.memory:! class: InMemoryStorageDriver ! services:! storage_driver:! alias: storage_driver.memory! services.yml services_test.yml The choice is coupled to the environment
  57. 57. 2- USING SYNTHETIC SERVICES AND ALIAS Define abstraction as “synthetic” services • Probably easy to setup for testing/dummy services Pros Cons • All services get defined, even when you are not going to use them • You have to define dependencies of services you probably not are going to use
  58. 58. ! namespace AcmeDemoBundleDependencyInjection;! ! use SymfonyComponentDependencyInjectionContainerBuilder;! use SymfonyComponentDependencyInjectionLoaderXmlFileLoader;! use SymfonyComponentHttpKernelDependencyInjectionExtension;! use SymfonyComponentConfigFileLocator;! ! class AcmeDemoExtension extends Extension! {! public function load(array $configs, ContainerBuilder $container)! {! $loader = new YamlFileLoader($container, new FileLocator(__DIR__.'/../Resources/config'));! $loader->load('services.yml');! }! ! public function getAlias()! {! return 'acme_demo';! }! }! services:! storage_driver:! synthetic: true! ! storage_driver.riak:! class: RiakStorageDriver! ! storage_driver.redis:! class: RedisStorageDriver! ! storage_driver.memory:! class: InMemoryStorageDriver! ! services:! storage_driver:! alias: storage_driver.redis! services.yml app/config/config.yml ! services:! storage_driver:! alias: storage_driver.memory! app/config/config_test.yml
  59. 59. 3- MANAGING SEMANTIC CONFIGURATIONS WITH EXTENSIONS • Instead of having the user override individual parameters, you let the user configure just a few, specifically created options. • As the bundle developer, you then parse through that configuration and load services inside an “Extension" • With this method, you won't need to import any configuration resources from your main application configuration: the Extension class can handle all of this
  60. 60. 3- MANAGING SEMANTIC CONFIGURATIONS WITH EXTENSIONS • Good fit if you are building a bundle to be used by 3rd parties and you have a lot of configuration options you want to validate • Lot of boilerplate code • Extra complexity added • You just wanted to manage dependency injection right?
  61. 61. class Configuration implements ConfigurationInterface! {! protected function addObjectStoreSection(ArrayNodeDefinition $rootNode)! {! $rootNode! ->children()! ->arrayNode('object_store')! ->isRequired()! ->children()! ->arrayNode('store_driver')! ->children()! ->scalarNode('type')->isRequired()->end()! ->scalarNode('connection')->end()! ->scalarNode('create_buckets')->end()! ->end()! ->validate()! ->ifTrue(function ($v) {! switch ($v['type']) {! case 'doctrine_dbal':! if (!isset($v['connection']) ||! !isset($v['create_buckets'])) {! return true;! }! break;! }! ! return false;! })! ->thenInvalid('children configuration')! ->end()! ->isRequired()! ->end()! ->end()! ->end();! }! } ! $definition = $container->getDefinition($storageDriver);! switch ($config['storage_driver']['type']) {! case 'doctrine_dbal':! $definition->replaceArgument(0, new Reference($config['storage_driver']['connection']));! $definition->replaceArgument(1, $config['storage_driver']['create_buckets']);! break;! case 'redis':! $definition->replaceArgument(0, new Reference($config['storage_driver']['connection']));! break;! }! ! $container->setAlias('object_storage.driver', $storageDriver);! Configuration Extension
  62. 62. 3- MANAGING SEMANTIC CONFIGURATIONS WITH EXTENSIONS • More powerful than simply defining parameters: a specific option value might trigger the creation of many service definitions; • Ability to have configuration hierarchy • Smart merging of several config files (e.g. config_dev.yml and config.yml) Pros Cons • Too much verbose, a lot of boilerplate code • Extra complexity added if you only want to define dependencies and not a long configuration tree !
  63. 63. 4- USING A CUSTOM INJECTOR • Let’s forget the Symfony DIC for a moment • Let’s go back to dependency management problem again
  64. 64. services:! ! order_processor:! ! ! class: OrderProcessor! arguments:! ! ! ! object_store: @object_store! ! ! ! order_repository: [mysql|cassandra] ! ! ! ! lock_system: [redis|zookeeper]! ! ! ! ! ! ! object_store:! ! ! class: ObjectStore! ! ! arguments:! ! ! storage_driver: [riak|redis|inmemory]! MySqlOrderRepository CassandraOrderRepository RedisLockSystem ZooKeeperLockSystem RedisStorageDriver InMemoryStorageDriver RiakStorageDriver
  65. 65. “A good architecture allows you to defer critical decisions, it doesn’t force you to defer them. However, if you can defer them, it means you have lots of flexibility” ! Uncle Bob
  66. 66. “A good architecture allows volatile decisions to be easily changed” ! Uncle Bob
  67. 67. services:! ! order_processor:! ! ! class: OrderProcessor! arguments:! ! ! ! object_store: @object_store! ! ! ! order_repository: [mysql|cassandra] ! ! ! ! lock_system: [redis|zookeeper]! ! ! ! ! ! ! object_store:! ! ! class: ObjectStore! ! ! arguments:! ! ! storage_driver: [riak|redis|inmemory]! MySqlOrderRepository CassandraOrderRepository RedisLockSystem ZooKeeperLockSystem RedisStorageDriver InMemoryStorageDriver RiakStorageDriver We need a dependency injection tool that allow us to easily change volatile decisions We need a dependency injection tool that allow us to defer critical decisions
  68. 68. Core Framework Payment Component Analytics Component Object Store Lock System Component Exports Depends On Unit Of Work Storage Driver Order Processor Product Repository Order Repository Payment Gateway Tracker Tracker Queue Implementations Redis, Zookeper Redis, C*, Riak, MySql Config, API MySql, C* Itunes, Facebook, Amazon, Google Play Redis, RabbitMQ, SQS, Kinesis
  69. 69. Core Component Object Store Lock System Component Exports Depends On Unit Of Work Storage Driver Implementations Redis, Zookeper Redis, C*, Riak, MySql namespace SPCoreGameFramework;! ! class FrameworkComponent implements Component! {! public function getName()! {! return 'core.game.framework';! }! ! public function getServicesDefinition()! {! return ServicesDefinition::create()! ! ->dependsOn('storage_driver')! ->withInstanceOf('SPCoreComponentObjectStoreStorageStorageDriver')! ! ->dependsOn('lock_system')! ->withInstanceOf('SPCoreComponentLockLockSystem')! ! ->exports('object_store')! ->withClass('SPCoreComponentObjectStore')! ->andConstructorDependencies(‘storage_driver’, ‘lock_system’);! }! } These are the decisions the component developer wants to defer Depends on abstractions, not concrete implementations
  70. 70. Payment Component Order Processor Product Repository Order Repository Config, API MySql, C* namespace SPCoreGamePayment;! ! class PaymentComponent implements Component! {! public function getName()! {! return 'core.game.payment';! }! ! public function getServicesDefinition()! {! return ServicesDefinition::create()! ! ! ! ! ->dependsOn('product_repository')! ->withInstanceOf('SPCoreGamePaymentProductRepositoryProductRepository')! ! ->dependsOn('order_repository')! ->withInstanceOf('SPCoreGamePaymentOrderRepositoryOrderRepository')! ! ->dependsOn('gateways')! ->withInstanceOf('GatewayDefinition')! ! ->exports(‘order_processor')! ->withClass('SPCoreGamePaymentOrderProcessor')! ->andConstructorDependencies(‘gateways', ‘product_repository’, ‘order_repository’);! }! } Itunes, Facebook, Amazon, Google Play Payment Gateway These are the decisions the component developer wants to defer Depends on abstractions, not concrete implementations
  71. 71. WHERE DOESTHE MAGIC COME FROM? • There is not such “magic” • Each component define it’s dependencies in a easy and legible way • Framework agnostic dependency definition • Based on the dependency definitions, services are added to the container during the container building phase
  72. 72. HOW? • First, collect services definitions from installed components • Second, inject services definitions into the Symfony (or Silex, or…) container • No magic, just code !!!
  73. 73. USING SYMFONY • Collect services definitions from installed components • Inject services definitions into the Symfony (or Silex, or…) container
  74. 74. use SymfonyComponentDependencyInjection as DI;! ! ! final class ComponentDependencyInjector implements DICompilerCompilerPassInterface! {! private $components;! ! public function __construct(array $components = array())! {! $this->components = $components;! }! ! public function process(ContainerBuilder $container)! {! foreach ($this->components as $component) {! $services = $component->getServicesDefinition();! foreach ($services->dependencies as $definition) {! $id = $component->getName() . '.' . $definition->name;! ! if (!$container->has($id)) {! throw new ServiceNotFoundException($component->getName(), $id, $definition->instanceOf);! }! }! }! }! ! public function registerComponentsDependencies(ContainerBuilder $container)! {! foreach ($this->components as $component) {! $this->addComponentDependencies($container, $component);! }! }! ! private function addComponentDependencies(ContainerBuilder $container, Component $component)! {! $container->addObjectResource($component);! $services = $component->getServicesDefinition();! foreach ($services->exports as $definition) {! $this->addDefinition($container, $definition, $component);! }! foreach ($services->definitions as $definition) {! $this->addDefinition($container, $definition, $component);! }! }! ! $def = new DIDefinition($definition->class, $args);! $def->setPublic($definition->public);! ! $container->setDefinition($component->getName() . '.' . $definition->name, $def);! }! }! The Component Dependency Injector responsibility is to inject the definitions in a given container
  75. 75. use SymfonyComponentHttpKernelKernel;! use SymfonyComponentConfigLoaderLoaderInterface;! ! class AppKernel extends Kernel! {! public function registerBundles()! {! $bundles = array(! new SymfonyBundleFrameworkBundleFrameworkBundle(),! new SymfonyBundleMonologBundleMonologBundle(),! ! new SPCoreBundleGameFrameworkBundleGameFrameworkBundle([! new SPCoreGameFrameworkFrameworkComponent(),! new SPCoreGameFrameworkPaymentComponent(),! new SPCoreGameFrameworkAnalyticsComponent(),! ]),! );! }! }! The AppKernel These are the framework agnostic components that provide infrastructure and logic for the application
  76. 76. namespace SPCoreBundleGameFrameworkBundle;! ! use SymfonyComponentDependencyInjectionCompilerPassConfig;! use SymfonyComponentHttpKernelBundleBundle;! use SymfonyComponentDependencyInjectionContainerBuilder;! ! use SPCoreBridgeSymfonyDependencyInjectionComponentDependencyInjector;! ! class GameFrameworkBundle extends Bundle! {! private $components;! ! function __construct(array $components = array())! {! $this->components = $components;! }! ! public function build(ContainerBuilder $container)! {! $injector = new ComponentDependencyInjector($this->components);! $injector->registerComponentsDependencies($container);! ! $container->addCompilerPass($injector, PassConfig::TYPE_BEFORE_REMOVING);! }! }! The (in)Famous Framework Bundle The components we are “installing” in this application The “magic” is here !!!
  77. 77. [SPCoreBridgeSymfonyDependencyInjectionExceptionServiceNotFoundException] Component "core.game.framework" requires the service "core.game.framework.lock_system" as an implementation of "SPCoreComponentLock LockSystem" but the service is not defined. [SPCoreBridgeSymfonyDependencyInjectionExceptionServiceNotFoundException] Component "core.game.payment" requires the service “core.game.payment.product_repository” as an implementation of "ProductRepository" but the service is not defined. $ php app/console The application complains about missing dependencies required by installed components We are planning to add suggested implementations for this requirement
  78. 78. services:! ! ! core.game.framework.lock_system:! ! ! public: false! ! ! class: SPCoreComponentLockRedisLockSystem! ! ! arguments:! redis: @sp.core.redis.connector.lock! timeout: 10! expiration: 10! config.yml services:! ! ! core.game.framework.lock_system:! ! ! public: false! ! ! class: SPCoreComponentLockMemoryLockSystem! ! ! arguments:! timeout: 10! expiration: 10! config_test.yml The application config Concrete implementation in the application (by default) Semantic configuration? Concrete implementation in the application (test mode)
  79. 79. 4- USING A CUSTOM INJECTOR • Complete control of component dependencies • Very limited in features (only constructor injections allowed) • Framework agnostic • Allows you to defer critical and volatile decisions Pros Cons • Very limited in features (only constructor injections allowed) ! !
  80. 80. CONCLUSIONS • You have the tools, use the best tool that solve your problems • Don’t be afraid of going to the limit with the framework you use • The framework is just an implementation detail
  81. 81. SOME REFERENCES http://www.objectmentor.com/resources/articles/dip.pdf ! http://www.martinfowler.com/articles/injection.html ! http://martinfowler.com/articles/dipInTheWild.html ! http://desymfony.com/ponencia/2013/inyeccion-dependencias-aplicaciones-php ! http://fabien.potencier.org/article/11/what-is-dependency-injection ! http://fabien.potencier.org/article/12/do-you-need-a-dependency-injection-container ! http://fabien.potencier.org/article/13/introduction-to-the-symfony-service-container ! https://www.youtube.com/watch?v=IKD2-MAkXyQ ! http://richardmiller.co.uk/2014/03/12/avoiding-setter-injection/ ! http://richardmiller.co.uk/2014/03/28/symfony2-configuring-different-services-for-different-environments/ ! http://www.infoq.com/news/2013/07/architecture_intent_frameworks ! http://blog.8thlight.com/uncle-bob/2012/08/13/the-clean-architecture.html !
  82. 82. THANK YOU For your attention @ronnylt

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