2.6. Dependency Injection

2.6.1. Zweck

Eine lose gekoppelte Architektur zu implementieren, um besser testbaren, wartbaren und erweiterbaren Code zu erreichen.

2.6.2. Verwendung

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.

2.6.3. Beispiele

• Das Doctrine2 ORM benutzt Dependency Injection für z.B. die Konfiguration, die in ein Connection injiziert wird. Für Testzwecke lässt sich diese leicht durch ein gemocktes Objekt austauschen.

• Viele Frameworks bieten bereits Dependency Injection Container an, die selbstständig vorkonfigurierte Objekte bei Bedarf erzeugen und diese in z.B. Controller injizieren können.

2.6.4. UML Diagramm

2.6.5. Code

Du findest den Code auch auf GitHub

DatabaseConfiguration.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Structural\DependencyInjection;

class DatabaseConfiguration
{
    public function __construct(
        private string $host,
        private int $port,
        private string $username,
        private string $password
    ) {
    }

    public function getHost(): string
    {
        return $this->host;
    }

    public function getPort(): int
    {
        return $this->port;
    }

    public function getUsername(): string
    {
        return $this->username;
    }

    public function getPassword(): string
    {
        return $this->password;
    }
}

DatabaseConnection.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Structural\DependencyInjection;

class DatabaseConnection
{
    public function __construct(private DatabaseConfiguration $configuration)
    {
    }

    public function getDsn(): string
    {
        // this is just for the sake of demonstration, not a real DSN
        // notice that only the injected config is used here, so there is
        // a real separation of concerns here

        return sprintf(
            '%s:%s@%s:%d',
            $this->configuration->getUsername(),
            $this->configuration->getPassword(),
            $this->configuration->getHost(),
            $this->configuration->getPort()
        );
    }
}

2.6.6. Теst

Tests/DependencyInjectionTest.php

<?php

declare(strict_types=1);

namespace DesignPatterns\Structural\DependencyInjection\Tests;

use DesignPatterns\Structural\DependencyInjection\DatabaseConfiguration;
use DesignPatterns\Structural\DependencyInjection\DatabaseConnection;
use PHPUnit\Framework\TestCase;

class DependencyInjectionTest extends TestCase
{
    public function testDependencyInjection()
    {
        $config = new DatabaseConfiguration('localhost', 3306, 'user', '1234');
        $connection = new DatabaseConnection($config);

        $this->assertSame('user:1234@localhost:3306', $connection->getDsn());
    }
}