Dependency injection in Drupal 8 : DrupalCon NOLA

Dependency injection in
Drupal 8
Ashwini Kumar

Who am I?
Ashwini Kumar
Tech Architect
@ashclimb

Agenda
✤ Mystery about DI
✤ Why to give my 2 cents to learn DI?
✤ DI in Symfony
✤ DI in Drupal 8

What is Dependency Injection?
Well, the literal meaning is injecting the dependency into
your Class.

Types of Dependency Injection
✤ Constructor Injection
✤ Setter Injection
✤ Property Injection

Constructor Injection
class NewsletterManager {
protected $mailer;
public function __construct(Mailer $mailer) {
$this->mailer = $mailer;
}
// ...
}

Setter Injection
protected $mailer;
public function setMailer(Mailer $mailer) {
$this->mailer = $mailer;
}
// ...
}

Property Injection
public $mailer;
// ...
}

Without dependency injection
class GoogleMaps {
public function getCoordinatesFromAddress($address) {
// calls Google Maps webservice
}
}
class OpenStreetMap {
public function getCoordinatesFromAddress($address) {
// calls OpenStreetMap webservice
}
}

class StoreService {
public function getStoreCoordinates($store) {
$geolocationService = new GoogleMaps();
// or $geolocationService = GoogleMaps::getInstance() if you use singletons
return $geolocationService->getCoordinatesFromAddress($store->getAddress());
}
}
Without dependency injection

With dependency injectionclass StoreService {
private $geolocationService;
public function __construct(GeolocationService $geolocationService) {
$this->geolocationService = $geolocationService;
}
public function getStoreCoordinates($store) {
return $this->geolocationService->getCoordinatesFromAddress($store-
>getAddress());
}
}

With dependency injection
interface GeolocationService {
public function getCoordinatesFromAddress($address);
}
class GoogleMaps implements GeolocationService { ...
class OpenStreetMap implements GeolocationService { ...

What we also get from this…
✤ Cleaner and Modular
✤ Reusable and Flexible
✤ Abstraction
✤ Testable

DI in a Framework
Dependency Injector
==
Dependency Injection Container(DIC)
==
IoC Container
==
Service Container
er

What is Service Container?
It basically deals with creating a map of your dependencies
which your class needs and check do we have it loaded?

Symfony’s Dependency injection
component

Symfony’s DI Component
✤ Services Keys are strings, e.g.
‘some_service’
✤ Service definitions in addition to specifying
which class to instantiate and what
constructor arguments to pass in, allow you
to specify additional methods to call on the
object after instantiation.

Symfony’s DI Component
✤ Default scope: Container
✤ Can be configured in PHP, XML or YAML
✤ Can be “compiled” down to plain PHP

Dependency Injection in Drupal 8

D8 Services mostly we will be using
✤ The default DB connection (‘database’)
✤ The module handler (‘module handler’)
✤ The HTTP request object (‘request’)

2 ways you can use core’s
services
1. Service location : From procedural code,
using a helper:
Drupal::service(‘some_service’)
2. DI way : Write OO code and get wired
into the container

How and Where does it all happen?
✤ The Drupal Kernel: code/lib/Drupal/Core/DrupalKernel.php
✤ Services are defined in : core/core.services.yml
✤ Compiler passes get added in: core/lib/Drupal/Core/CoreBundle.php
✤ Compiler pass classes live here:
core/lib/Drupal/Core/DependenciesInjection/compiler/…

How does it happen for my Module?
✤ Services are defined in : mymodule/mymodule.services.yml
✤ Compiler passes get added in: my
module/lib/Drupal/mymodule/MymoduleBundle.php
✤ All classes, including compiler pass classes must live in : my
module/lib/Drupal/mymodule/

What Magic do we have in *.services.yml ?
services:
# Defines a simple service of which requires no parameter for its constructor.
example.simple:
class: DrupalExampleSimple
# Defines a service which requires the module_handler for its constructor.
example.with_module_handler
class: DrupalExampleWithModuleHandler
arguments: ['@module_handler']

Implement:Dependency Injection for a Form

https://api.drupal.org/api/drupal/services

“Start Small, then work your way up!”
~ The person who is quoted

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Dependency injection in Drupal 8 : DrupalCon NOLA

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