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

How we want our code to look like?

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How we want our code to look like?

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How It Actually Looks

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●

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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

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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Example !

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Defining the Services :

services:

example.access_checker:

class:

Drupal\example\Access\CustomAccessCheck

arguments: ['@current_user']

tags:

- { name: access_check, applies_to:

_example_access_check }

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namespace Drupal\example\Access;

use Drupal\Core\Routing\Access\AccessInterface;

use Drupal\Core\Session\AccountInterface;

class CustomAccessCheck implements AccessInterface {

/**

* A custom access check.

*

* @param \Drupal\Core\Session\AccountInterface $account

* Run access checks for this account.

*/

public function access(AccountInterface $account) {

return $account->hasPermission('custom_permission’);

}

}

What are services and services container?

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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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Goal : We want to write a code that is :● Reusable● Clutter Free● Testeable

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The less your code knows, the more reusable it is!

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Core Services in Drupal 8

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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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Creating Services in Custom Module

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● 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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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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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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Questions

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