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Services, dependency injection and containers

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Sushil Hanwate
Sushil Hanwate

This document discusses services, dependency injection, and containers in Drupal 8. It defines a service as any PHP object that performs a global task. Services are defined in *.services.yml files and can be obtained either through service location from outside classes or through dependency injection inside classes. Dependency injection involves passing services as references into dependent objects to decouple classes and allow for loose coupling and testability. Services can also be overridden by defining new classes that implement the necessary interfaces and registering them as replacements.

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Services, Dependency Injection and Containers In Drupal 8
About Me Sushil Hanwate Twitter: @thesushyl Drupal Developer @
What is a Service? A Service is any PHP object that performs some sort of "global" task. It's a purposefully-generic name used in computer science to describe an object that's created for a specific purpose (e.g. delivering emails). As a rule, a PHP object is a service if it is used globally in your application.
Defining Services // user.services.yml services: access_check.permission: class: DrupaluserAccessPermissionAccessCheck // ¡®modules/user/src/access/PermissionAccessCheck.php¡¯ tags: - { name: access_check, applies_to: _permission } // core.services.yml services: path.alias_manager: class: DrupalCorePathAliasManager // ¡®/core/lib/drupal/core/path/AliasManager.php¡¯ arguments: ['@path.alias_storage', '@path.alias_whitelist', '@language_manager', '@cache.data']
Obtaining Services Service Location (Procedural) Dependency Injection (Used in classes)
Obtaining Services: Service Location // Get service from outside of a class. $service = Drupal::service('service_name'); // If you have $container variable $service = $container->get('service_name'); // Example services $cache = Drupal::cache(); $lock = Drupal::lock()->acquire($lock_name)
Obtaining Services: Service Location // Source $cache = Drupal::cache();
Dependency Injection - Definition Dependency injection is a software design pattern in which one or more dependencies/services are injected, or passed by reference , into a dependent object/client and are made part of the client's state. The pattern separates the creation of a client's dependencies from its own behavior, which allows program designs to be loosely coupled and to follow the dependency inversion and single responsibility principles.
Obtaining Services: Dependency Injection 1. DI is used in classes. 2. If your class is a service, inject dependencies via arguments in *.services.yml services: path.alias_manager: class: DrupalCorePathAliasManager // ¡®/core/lib/drupal/core/path/AliasManager.php¡¯ arguments: ['@path.alias_storage', '@path.alias_whitelist', '@language_manager', '@cache.data'] // code public function __construct (AliasStorageInterface $storage, AliasWhitelistInterface $whitelist, LanguageManagerInterface $language_manager, CacheBackendInterface $cache) {
Overriding Services 1. Locate default class and interface 2. Define a class that provides same services with different way implementing interface and/or overriding the class, say Drupalfoo_barMyNewServiceClass 1. Define a class that implements DrupalCoreDependencyInjectionServiceModifierInterface called Drupalfoo_barFooBarServiceProvider 2. Put this in alter() method public function alter(ContainerBuilder $container) { $definition = $container->getDefinition('service.name'); $definition->setClass(Drupalfoo_barMyNewServiceClass); }
Why Dependency Injection? Clutter-free Re-usable Testable
References 1.http://www.slideshare.net/katbailey/di-drupal8 2.https://www.youtube.com/watch?v=TAXgizY-p4k 3.https://docs.acquia.com/articles/drupal-8-dependency- injection
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Services, dependency injection and containers

  • 1. Services, Dependency Injection and Containers In Drupal 8
  • 2. About Me Sushil Hanwate Twitter: @thesushyl Drupal Developer @
  • 3. What is a Service? A Service is any PHP object that performs some sort of "global" task. It's a purposefully-generic name used in computer science to describe an object that's created for a specific purpose (e.g. delivering emails). As a rule, a PHP object is a service if it is used globally in your application.
  • 4. Defining Services // user.services.yml services: access_check.permission: class: DrupaluserAccessPermissionAccessCheck // ¡®modules/user/src/access/PermissionAccessCheck.php¡¯ tags: - { name: access_check, applies_to: _permission } // core.services.yml services: path.alias_manager: class: DrupalCorePathAliasManager // ¡®/core/lib/drupal/core/path/AliasManager.php¡¯ arguments: ['@path.alias_storage', '@path.alias_whitelist', '@language_manager', '@cache.data']
  • 5. Obtaining Services Service Location (Procedural) Dependency Injection (Used in classes)
  • 6. Obtaining Services: Service Location // Get service from outside of a class. $service = Drupal::service('service_name'); // If you have $container variable $service = $container->get('service_name'); // Example services $cache = Drupal::cache(); $lock = Drupal::lock()->acquire($lock_name)
  • 7. Obtaining Services: Service Location // Source $cache = Drupal::cache();
  • 8. Dependency Injection - Definition Dependency injection is a software design pattern in which one or more dependencies/services are injected, or passed by reference , into a dependent object/client and are made part of the client's state. The pattern separates the creation of a client's dependencies from its own behavior, which allows program designs to be loosely coupled and to follow the dependency inversion and single responsibility principles.
  • 9. Obtaining Services: Dependency Injection 1. DI is used in classes. 2. If your class is a service, inject dependencies via arguments in *.services.yml services: path.alias_manager: class: DrupalCorePathAliasManager // ¡®/core/lib/drupal/core/path/AliasManager.php¡¯ arguments: ['@path.alias_storage', '@path.alias_whitelist', '@language_manager', '@cache.data'] // code public function __construct (AliasStorageInterface $storage, AliasWhitelistInterface $whitelist, LanguageManagerInterface $language_manager, CacheBackendInterface $cache) {
  • 10. Overriding Services 1. Locate default class and interface 2. Define a class that provides same services with different way implementing interface and/or overriding the class, say Drupalfoo_barMyNewServiceClass 1. Define a class that implements DrupalCoreDependencyInjectionServiceModifierInterface called Drupalfoo_barFooBarServiceProvider 2. Put this in alter() method public function alter(ContainerBuilder $container) { $definition = $container->getDefinition('service.name'); $definition->setClass(Drupalfoo_barMyNewServiceClass); }