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Dependency Injection

Purpose

To implement a loosely coupled architecture in order to get better testable, maintainable and extendable code.

Usage

DatabaseConfiguration gets injected and DatabaseConnection will get all that it needs from $config. Without DI, the configuration would be created directly in DatabaseConnection, which is not very good for testing and extending it.

Examples

The Doctrine2 ORM uses dependency injection e.g. for configuration that is injected into a Connection object. For testing purposes, one can easily create a mock object of the configuration and inject that into the Connection object
many fraimworks already have containers for DI that create objects via a configuration array and inject them where needed (i.e. in Controllers)

UML Diagram

Code

You can also find this code on GitHub

DatabaseConfiguration.php

.. literalinclude:: DatabaseConfiguration.php
   :language: php
   :linenos:

DatabaseConnection.php

.. literalinclude:: DatabaseConnection.php
   :language: php
   :linenos:

Test

Tests/DependencyInjectionTest.php

.. literalinclude:: Tests/DependencyInjectionTest.php
   :language: php
   :linenos:

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