1. 设计模式
  2. 扩展模式
  3. 依赖注入模式

依赖注入模式

目的

为了实现松散耦合的架构，以获得更好的可测试、可维护和可扩展的代码。

用法

下面的代码定义了 DatabaseConfiguration 类，该类的实例将被注入到 DatabaseConnection 对象中。DatabaseConnection 会从注入的 DatabaseConfiguration 中获取所有需要的变量。如果不使用依赖注入的方式，数据库配置对象将直接在 DatabaseConnection 中创建，这不利于测试和扩展。

使用场景

  • Doctrine2 中的 ORM 使用了依赖注入。例如，它使用的配置是注入到 Connection 对象中的。为了方便测试，我们可以很轻松地创建一个模拟配置对象，并将其注入到 Connection 对象中
  • 许多框架已经实现了依赖注入容器，通过配置数组来创建对象，并在需要的地方注入它们（例如，在控制器中）

UML 类图

依赖注入模式类图

代码

DatabaseConfiguration.php

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<?php declare(strict_types = 1);

namespace DesignPatterns\Extend\DependencyInjection;

class DatabaseConfiguration
{
    private string $host;
    private int $port;
    private string $username;
    private string $password;

    public function __construct(string $host, int $port, string $username, string $password)
    {
        $this->host = $host;
        $this->port = $port;
        $this->username = $username;
        $this->password = $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

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<?php declare(strict_types = 1);

namespace DesignPatterns\Extend\DependencyInjection;

class DatabaseConnection
{
    private DatabaseConfiguration $configuration;

    public function __construct(DatabaseConfiguration $config)
    {
        $this->configuration = $config;
    }

    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()
        );
    }
}

测试

Tests/DependencyInjectionTest.php

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<?php declare(strict_types = 1);

namespace DesignPatterns\Extend\DependencyInjection\Tests;

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

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

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