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Service container

A service containerĀ (aka Dependency Injection Container, DIC) is a special object that facilitates dependency resolution. It is based on the dependency injection design pattern.

Dependency injection proposes to inject all needed objects and configuration into your business logic objects (known as services). It avoids the massive use of singletons, global variables or complicated factories and makes your code much more readable and testable.

The main issue with this pattern is how to resolve the dependencies for your services. This is where the service container comes into play. The role of a service container is to build and maintain your services and their dependencies. Each time you need a service, you may ask the service container for it. It will either build the service with the configuration you provided, or give you an existing instance if it is already available.

eZ Platform uses theĀ Symfony service container.

Tip

To learn more about the service container, see:

Service tags

Service tags in Symfony DIC are a useful way of dedicating services to a specific purpose. They are usually used for extension points.

For instance, if you want to register a Twig extension to add custom filters, you need to create the PHP class and declare it as a service in the DIC configuration with the twig.extension tag (see the Symfony cookbook entry for a full example).

eZ Platform exposes several features this way (see the list of core service tags). This is for example the case with Field Types.

You will find all service tags exposed by Symfony in its reference documentation.

Core and API

Tag name Usage
router Adds a specific router to the chain router
twig.loader Registers a template loader for Twig
ezpublish.content_view_provider Registers a ContentViewProvider for template selection depending on content/Location being viewed
ezpublish.storageEngine Registers a storage engine in the Repository factory
ezpublish.fieldType Registers a Field Type

Legacy

Tag name Usage
ezpublish.storageEngine.legacy.converter Registers a converter for a Field Type in Legacy storage engine
ezpublish.fieldType.externalStorageHandler Registers an external storage handler for a Field Type
ezpublish.fieldType.externalStorageHandler.gateway Registers an external storage gateway for a Field Type in Legacy storage engine
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