php – 使用DI容器替换全局$注册表对象是否可行？

Q2：
如果你传递你的$注册表对象….所以你的注册表并不是所谓的注册表(正如福勒描述的).

注册表或多或少是具有get / set方法的全局对象(“众所周知的”).
在PHP中,两个用于实现注册表的常见原型是

作为单身人士

class RegistryAsSingleton
{
    public static function getInstance (){
       //the singleton part
    }

    public function getStuff ()
    {
       //some stuff accessed thanks to the registry
    }
}

用静态方法遍布各地

class RegistryAsStatic
{
    public static function getStuff()
    {
    }
}

将注册表传递到整个地方使得它只是一个对象：一个容器,而不是提供对其他对象的引用的目的.

您的DI容器(使用Pimple,如您在OP中建议的)是一种注册表本身：它是众所周知的,使您能够从任何地方获取组件.

所以是的,我们可以说您的DI容器将通过执行相同的功能来删除注册表的要求和必要性.

但是(总是有一个但是)

Registry are always guilty until
proven innocent
(Martin Fowler)

如果您正在使用DI Container替换注册表,这可能是错误的.

例如：

//probably a Wrong usage of Registry
class NeedsRegistry
{
    public function asAParameter(Registry $pRegistry)
    {
       //Wrong dependency on registry where dependency is on Connection
       $ct = $pRegistry->getConnection();
    }

    public function asDirectAccess ()
    {
       //same mistake,more obvious as we can't use another component
       $ct = Registry::getInstance()->getConnection();
    }
}

//probably a wrong replacement for Registry using DI Container
class NeedsContainer
{
    public function asAParameter(Container $pRegistry)
    {
       //We are dependent to the container with no needs,//this code should be dependent on Connection
       $ct = $pContainer->getConnection();
    }

    public function asDirectAccess ()
    {
       //should not be dependent on container
       $ct = Container::getInstance()->getConnection();
    }
}

为什么这样坏？因为你的代码比以前更少的依赖,它仍然依赖于一个组件(一个注册表或一个容器),它没有提供一个明确的目标(我们可能会想到这里的接口)

注册表模式在某些情况下是有用的,因为它是一种简单且相当便宜的方法来定义组件或数据(例如全局配置).

通过删除依赖关系来重构上述示例而不依赖于DI的方式将是：

class WasNeedingARegistry
{
    public function asAParameter (Connection $pConnection)
    {
       $pConnection->doStuff();//The real dependency here,we don't care for 
       //a global registry
    }
}

//the client code would be like
$wasNeedingARegistry = new WasNeedingARegistry();
$wasNeedingARegistry->setConnection($connection);

当然,如果客户端代码不知道连接,这可能是不可能的,这可能是您可能首先使用注册表结束的原因.

现在DI发挥作用

使用DI使我们的生活更美好,因为它将处理依赖关系,并使我们能够在即时使用状态下访问依赖关系.

您代码中的某个地方,您将配置您的组件：

$container['connection'] = function ($container) {
    return new Connection('configuration');
};
$container['neededARegistry'] = function ($container) {
    $neededARegistry = new NeededARegistry();
    $neededARegistry->setConnection($container['connection']);
    return $neededARegistry;
};

现在你拥有重构代码所需的一切：

// probably a better design pattern for using a Registry 
class NeededARegistry
{
    public function setConnection(Connection $pConnection)
    {
       $this->connection = $pConnection;
       return $this;
    }

    public function previouslyAsDirectAccess ()
    {
       $this->connection->doStuff();
    }
}

//and the client code just needs to know about the DI container
$container['neededARegistry']->previouslyAsDirectAccess();

“客户端”代码应尽可能隔离.客户端应该负责并注入自己的依赖项(通过设置方法).客户端不应负责处理其依赖关系.

class WrongClientCode
{
    private $connection;
    public function setConnection(Connection $pConnection)
    {
       $this->connection = $pConnection;
    }

    public function callService ()
    {
       //for the demo we use a factory here
       ServiceFactory::create('SomeId')
                       ->setConnection($this->connection)
                       ->call();
       //here,connection was propagated on the solely 
       // purpose of being passed to the Service
    }
}

class GoodClientCode
{
    private $service;
    public function setService(Service $pService)
    {
       //the only dependency is on Service,no more connection
       $this->service = $pService;
    }

    public function callService ()
    {
       $this->service->setConnection($this->connection)
                     ->call();
    }
}

DI容器将配置已经使用其连接正确配置的服务的GoodClientCode

对于Singleton方面,是的,它将使你摆脱它们.希望这可以帮助