The introduction of Object Oriented Programming in Drupal 8 is an evolution in the world of Drupal which has brought the concept of code reuse and encapsulation, allowing users to build better maintainable and structured code. One of the concepts that contribute to this is Dependency Injection and Services in Drupal Is there a way for someone to modify the process by which Drupal invokes modules without making changes to the core function in Drupal 7? Or is there a better way to access the global variables without calling them directly in Drupal 7? The answer is “No”. This session aims at understanding the dependency injection and services in Drupal 8, that may be a bit complex but are really usable.

1. Demystifying Dependency Injection
And Services In Drupal 8
Jyoti Singh | Developer| Srijan Technologies
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● Problems in Drupal 7
● Dependency Injection
● Services and Services Container
● Drupal 8 core services and how to use them.
● Using Services in contributed module.
Objective Of The Session

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Why Dependency Injection

4. How we want our code to look
like?
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5. How we want our code to look
like?
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6. How It Actually Looks
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7. ●
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Problems In Drupal 7!

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● No way to Reuse the code (not
OVERRIDE)
● - for eg : Copy the callback entirely and
replace it with your code.

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How can we test something?
- Create mock objects? NO.
- Want a simple test class? Bootstrap
Drupal first.

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Lot of Cluttering Happens
- Excessive use of alter hooks
- preprocess for calculations
- PHP in template files

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Let’s take a wrong approach

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Some procedural code
*foo_bar knows about the user object.
*node_make_me_look_cool needs a function from another module.
*You need bootstrapped Drupal to use module_load_include, or at least include the file that
declares it.
*foo_bar assumes some default database connection.

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User class uses sessions to store
language

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What Is Dependency Injection?

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Dependency injection is an advanced software
design pattern. It implements “inversion of
control”, which means that reusable code calls
task specific code.

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What does this mean for us Drupal
developers?
It means we can write more efficient code by
reducing the load. We only load what we need.
Type Of Injections

18. Type Of Injections
Constructor injection
Setter injection
property injection
Setter injectionSetter injection
class User
{
function setSessionStorage($storage)
{
$this->storage = $storage;
}
}
class User
{
public $sessionStorage;
}
$user->sessionStorage = $storage;
class User
{
function construct($storage) {
$this->storage = $storage;
}
}
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19. Example !
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20. Defining the Services :
services:
example.access_checker:
class:
DrupalexampleAccessCustomAccessCheck
arguments: ['@current_user']
tags:
- { name: access_check, applies_to:
_example_access_check }
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namespace DrupalexampleAccess;
use DrupalCoreRoutingAccessAccessInterface;
use DrupalCoreSessionAccountInterface;
class CustomAccessCheck implements AccessInterface {
/**
* A custom access check.
*
* @param DrupalCoreSessionAccountInterface $account
* Run access checks for this account.
*/
public function access(AccountInterface $account) {
return $account->hasPermission('custom_permission’);
}
}

21. What are services and services
container?
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22. Service is simply an object, usually with one
instance of each service's class for each
service on a site. For example, Drupal 8 sites
have a service for sending email, for logging
errors, for making HTTP requests, and
dozens of other common tasks.
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23. Goal : We want to write a code that is :
● Reusable
● Clutter Free
● Testeable
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24. The less your code knows, the
more reusable it is!
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25. Core Services in Drupal 8
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26. Some of the commonly used services in Drupal 8 core are :
● entity.query and entity.manager – Services use to access the
informationa about Drupal entities.
● config.fatory – Loads the Config information out of your Drupal
site
● config.storage - Service that knows where to store variables on
your site
● config.typed - Helps to store different data types in config
object.
● event_dispatcher - helps to "lazy load" classes so loading code
and instantiating objects only happens when the objects are
actually needed.
● current_user – The service that provides data for the drupal
user.
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27. Creating Services in
Custom Module
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28. ● Create a src Folder inside the custom module.
● Create a EvenSubscriber Class inside the src
Folder
● Implement the EventSubscriberInterface .
● Implement some of the basic functions of
EventSubscriberInterface like onRespond() and
getSubscribedEvents()
● Create a services.yml file inside the root folder of
the custom module.
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29. This is how the EvenSubscriber Class looks like :
class ZipangSubscriber implements EventSubscriberInterface {
public function onRespond(FilterResponseEvent $event) {
$response = $event->getResponse();
$response->headers->set('X-Custom-Header', '******');
}
public static function getSubscribedEvents() {
$events[KernelEvents::RESPONSE][] = array('onRespond');
return $events;
}
}
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30. Service Tags
Tags are used to define a group of related services,
or to specify some aspect of how the service
behaves.
Some of the tags used are :
● event_subscriber: Indicates an event subscriber
service.
● access_check: Indicates a route access checking
service;
● cache.bin: Indicates a cache bin service,etc
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31. Questions
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