Dependency Injection in Drupal 8

What is Dependency Injection?

Injecting the dependency into your class

Types of Dependency Injection

  • Constructor
    • Pass dependency as paramater of the __construct method of the class
    • Mandatory dependency
  • Setter
    • Pass into a setter method in the class
    • Optional dependency
    • Cannot control dependency lifetime in the class
  • Property
    • Similar to setter
    • Pass into a public property of the class.


  • Cleaner and modular code
  • Reusable and flexible
  • Abstracted
  • Testable

DI in a Framework

Dependency injection == Dependency injection Container (DIC) == IOC Container == Service Container

What is a Service Container?

Creates a map of dependencies that classes need and handle loading/unloading

Symfony DI

  • Services keys are strings e.g. ‘some_service’
  • Service definitions specify which class to instantiate, the arguments to pass and additional methods to call on the object after instantiation
  • Configure in PHP, XML or YAML
    • Can be ‘compiled’ down to PHP

Drupal 8 DI

2 ways to use core services:

  • Service location: Used for procedural code e.g. Drupal::service('some_service')
  • Service container: Used for OO code e.g. $container->get('some_service')

How and Where?

  • Core services defined in core/
  • Custom services defined in mymodule/
  • Custom classes live in mymodule/lib/Drupal/mymodule
  • List of core services can be found at