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DIC To The Limit – deSymfonyDay, Barcelona 2014

This document provides an overview of dependency injection and dependency injection containers. It discusses the problems that dependency injection aims to solve, such as having interchangeable implementations for different environments. It covers dependency inversion principles, types of dependency injection like constructor injection, and using a dependency injection container like Symfony's to automate object instantiation and wiring of dependencies. The document aims to explain how dependency injection can help decouple classes and make code more testable and reusable across different deployments.

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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 ! @ronnylt
 www.tangotree.io
 https://github.com/ronnylt
AGENDA • The problems • Dependency Injection • Coupling done right • Dependency Inversion Principle • Types of DI • Dependency Injection Containers • Symfony Dependency Injection Container • Interchangeable Services
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
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 Principles
WHAT WE REALLY WANT IS • Code that is easy to test • Clear separation of infrastructure logic from application logic • Interchangeable infrastructure
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…
“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 None Coupling is a measure of the independency of components/modules
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
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
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 ZooKeeperLockSystem <<interface>> <<interface>> ObjectStore RedisStorageDriver InMemoryStorageDriver RiakStorageDriver StorageDriver <<interface>>
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 ! class EnergyBuyCommandHandler implements CommandHandler! {! private $playerRepository;! ! private $configRepository;! ! public function __construct(! ! ! PlayerRepository $playerRepository, ! ! ! ConfigRepository $config! ! )! {! $this->playerRepository = $playerRepository;! $this->configRepository = $config;! }! }!
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
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
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;! }! }!
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
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
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
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)! {! }! }!
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 $mailer;! ! // ...! }!
PROPERTY INJECTION • Useful if you are working with code that is out of your control, such as in a 3rd party library, which uses public properties for its dependencies Pros Cons • You cannot control when the dependency is set at all, it can be changed at any point in the object's lifetime • You cannot use type hinting so you cannot be sure what dependency is injected except by writing into the class code to explicitly test the class instance before using it
SERVICES LOCATOR • Is an object that knows how to get all of the services that an another service might need interface CommandHandlerLocator ! {! public function locate($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);! }! }!
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)
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
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 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
DEPENDENCY INJECTION CONTAINERS IN PHP
PHP DIC IMPLEMENTATIONS • Twittee • Pimple • IlluminateDi • ZendDi • SymfonyDependencyInjection • http://php-di.org/ • Build your own
SYMFONY 
 DEPENDENCY INJECTION CONTAINER
The Dependency Injection component allows you to standardize and centralize the way objects are constructed in a SF application
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
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 comfortable creating your own objects via the container • So, let’s try to solve the problems we stated at the beginning
INTERCHANGEABLE SERVICES
OrderProcessor OrderRepository MySqlOrderRepository CassandraOrderRepository LockSystem RedisLockSystem ZooKeeperLockSystem <<interface>> <<interface>> ObjectStore RedisStorageDriver InMemoryStorageDriver RiakStorageDriver StorageDriver <<interface>>
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! {}!
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
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
SERVICES SETUP Deployment Environment Concrete Implementation DRAGON TESTING in-memory DRAGON STAGING/QA redis DRAGON PROD mysql MONSTER TESTING in-memory MONSTER PROD cassandra
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
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
! 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
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
! 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
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
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?
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
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 !
4- USING A CUSTOM INJECTOR • Let’s forget the Symfony DIC for a moment • Let’s go back to dependency management problem again
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
“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
“A good architecture allows volatile decisions to be easily changed” ! Uncle Bob
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
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
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
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
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
HOW? • First, collect services definitions from installed components • Second, inject services definitions into the Symfony (or Silex, or…) container • No magic, just code !!!
USING SYMFONY • Collect services definitions from installed components • Inject services definitions into the Symfony (or Silex, or…) container
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
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
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 !!!
[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
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)
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) ! !
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
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 !
THANK YOU For your attention @ronnylt

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DIC To The Limit – deSymfonyDay, Barcelona 2014

  • 1.
  • 3.
    Ronny López ABOUT MEUS Hard way learner ! Technical Lead at Social Point Do stuff atTangoTree in the nights ! @ronnylt
 www.tangotree.io
 https://github.com/ronnylt
  • 4.
    AGENDA • The problems •Dependency Injection • Coupling done right • Dependency Inversion Principle • Types of DI • Dependency Injection Containers • Symfony Dependency Injection Container • Interchangeable Services
  • 5.
    THE PROBLEMS • Werequire 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
  • 6.
    YAGNI You aren't gonnaneed it, let’s go home!
  • 7.
    IN CASEYOU NEEDIT • You have to do Dependency Injection, correctly • You have to know and apply Dependency Inversion Principles
  • 8.
    WHAT WE REALLYWANT IS • Code that is easy to test • Clear separation of infrastructure logic from application logic • Interchangeable infrastructure
  • 9.
    WHY? • Multiple deploymentsshare 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…
  • 11.
    “The only wayto go fast, is to go well”
 Uncle Bob
  • 12.
  • 13.
    Dependency injection isa simple way to decouple classes from what they depend on
  • 14.
    Dependency injection decouples classes constructionfrom the construction of it’s dependencies
  • 15.
    IS IT ALLABOUT COUPLING?
  • 16.
    COUPLING Mod A ModB 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
  • 17.
    COUPLING • The historyof 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
  • 18.
    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
  • 19.
  • 20.
    High-level modules should notdepend on low-level modules. Both should depend on abstractions
  • 21.
    Abstractions should not dependon details. Details should depend on abstractions
  • 22.
    DEPENDENCY INVERSION • Decouplehigh level parts of the system from low level parts by using interfaces
  • 23.
  • 24.
  • 25.
    TYPES OF DI •Constructor Injection • Setter Injection • Interface Injection • Property Injection • Service Locator
  • 26.
    CONSTRUCTOR INJECTION • Injectsthe 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;! }! }!
  • 27.
    CONSTRUCTOR INJECTION • Itensures 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
  • 28.
    CONSTRUCTOR INJECTION • Tryto 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
  • 29.
    SETTER INJECTION • Injectthe 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;! }! }!
  • 30.
    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
  • 31.
    SETTER INJECTION TIPS • Avoidsetter 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
  • 32.
    SETTER INJECTION EXAMPLE use PsrLogLoggerInterface;! ! finalclass 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
  • 33.
    INTERFACE INJECTION • Defineand 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)! {! }! }!
  • 34.
    PROPERTY INJECTION • Allowssetting 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 $mailer;! ! // ...! }!
  • 35.
    PROPERTY INJECTION • Usefulif you are working with code that is out of your control, such as in a 3rd party library, which uses public properties for its dependencies Pros Cons • You cannot control when the dependency is set at all, it can be changed at any point in the object's lifetime • You cannot use type hinting so you cannot be sure what dependency is injected except by writing into the class code to explicitly test the class instance before using it
  • 36.
    SERVICES LOCATOR • Isan object that knows how to get all of the services that an another service might need interface CommandHandlerLocator ! {! public function locate($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);! }! }!
  • 37.
    SERVICE LOCATOR • It’seasy 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)
  • 38.
    SERVICE LOCATOR TIPS • Usea segregated interface for the locator, do not depends on the whole locator (container) ! • Limit the types of services a locator provides
  • 39.
  • 40.
    Dependency Injection Container issimply an object that manages the instantiation of other objects
  • 41.
    Automagically creates a giventype with all the required dependencies
  • 42.
    DIC • Most ofthe 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
  • 43.
  • 44.
    PHP DIC IMPLEMENTATIONS •Twittee • Pimple • IlluminateDi • ZendDi • SymfonyDependencyInjection • http://php-di.org/ • Build your own
  • 45.
  • 46.
    The Dependency Injection componentallows you to standardize and centralize the way objects are constructed in a SF application
  • 47.
    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
  • 48.
    ADVANCED HOW IT WORKS •Compiler Passes • Container Extensions • Services Configurator • Tagged Services
  • 49.
    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
  • 50.
  • 51.
  • 52.
    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! {}!
  • 53.
    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
  • 54.
    THE PROBLEM • It’snot 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
  • 55.
    SERVICES SETUP Deployment EnvironmentConcrete Implementation DRAGON TESTING in-memory DRAGON STAGING/QA redis DRAGON PROD mysql MONSTER TESTING in-memory MONSTER PROD cassandra
  • 56.
    SOLUTIONS 1. Loading differentconfigurations depending on the environment and aliasing services 2. Using synthetic services and aliases 3. Managing semantic configuration with extensions 4. Using a custom injector
  • 57.
    1- LOADING DIFFERENTCONFIGURATIONS 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
  • 58.
    ! namespace AcmeDemoBundleDependencyInjection;! ! use SymfonyComponentDependencyInjectionContainerBuilder;! useSymfonyComponentDependencyInjectionLoaderXmlFileLoader;! 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
  • 59.
    2- USING SYNTHETICSERVICES 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
  • 60.
    ! namespace AcmeDemoBundleDependencyInjection;! ! use SymfonyComponentDependencyInjectionContainerBuilder;! useSymfonyComponentDependencyInjectionLoaderXmlFileLoader;! 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
  • 61.
    3- MANAGING SEMANTICCONFIGURATIONS 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
  • 62.
    3- MANAGING SEMANTICCONFIGURATIONS 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?
  • 63.
    class Configuration implementsConfigurationInterface! {! 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
  • 64.
    3- MANAGING SEMANTICCONFIGURATIONS 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 !
  • 65.
    4- USING ACUSTOM INJECTOR • Let’s forget the Symfony DIC for a moment • Let’s go back to dependency management problem again
  • 66.
    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
  • 67.
    “A good architectureallows 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
  • 68.
    “A good architectureallows volatile decisions to be easily changed” ! Uncle Bob
  • 69.
    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
  • 70.
    Core Framework Payment Component AnalyticsComponent 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
  • 71.
    Core Component ObjectStore 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
  • 72.
    Payment Component OrderProcessor 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
  • 73.
    WHERE DOESTHE MAGICCOME 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
  • 74.
    HOW? • First, collectservices definitions from installed components • Second, inject services definitions into the Symfony (or Silex, or…) container • No magic, just code !!!
  • 75.
    USING SYMFONY • Collectservices definitions from installed components • Inject services definitions into the Symfony (or Silex, or…) container
  • 76.
    use SymfonyComponentDependencyInjection asDI;! ! ! 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
  • 77.
    use SymfonyComponentHttpKernelKernel;! use SymfonyComponentConfigLoaderLoaderInterface;! ! classAppKernel 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
  • 78.
    namespace SPCoreBundleGameFrameworkBundle;! ! use SymfonyComponentDependencyInjectionCompilerPassConfig;! useSymfonyComponentHttpKernelBundleBundle;! 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 !!!
  • 79.
    [SPCoreBridgeSymfonyDependencyInjectionExceptionServiceNotFoundException] Component "core.game.framework" requiresthe 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
  • 80.
    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)
  • 81.
    4- USING ACUSTOM 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) ! !
  • 82.
    CONCLUSIONS • You havethe 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
  • 83.
    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 !
  • 84.
    THANK YOU For yourattention @ronnylt