如何定义抽象类和接口之间的关系

// src/Acme/AppBundle/Entity/Customer.php
 
namespace Acme\AppBundle\Entity;
 
use Doctrine\ORM\Mapping as ORM;
use Acme\CustomerBundle\Entity\Customer as BaseCustomer;
use Acme\InvoiceBundle\Model\InvoiceSubjectInterface;
 
/**
 * @ORM\Entity
 * @ORM\Table(name="customer")
 */
class Customer extends BaseCustomer implements InvoiceSubjectInterface
{
    // In this example, any methods defined in the InvoiceSubjectInterface
    // are already implemented in the BaseCustomer
    // 本例中，任何定义于InvoiceSubjectInterface中的方法皆已被BaseCustomer所实现
}

// src/Acme/InvoiceBundle/Entity/Invoice.php
 
namespace Acme\InvoiceBundle\Entity;
 
use Doctrine\ORM\Mapping AS ORM;
use Acme\InvoiceBundle\Model\InvoiceSubjectInterface;
 
/**
 * Represents an Invoice.
 *
 * @ORM\Entity
 * @ORM\Table(name="invoice")
 */
class Invoice
{
    /**
     * @ORM\ManyToOne(targetEntity="Acme\InvoiceBundle\Model\InvoiceSubjectInterface")
     * @var InvoiceSubjectInterface
     */
    protected $subject;
}

// src/Acme/InvoiceBundle/Model/InvoiceSubjectInterface.php
 
namespace Acme\InvoiceBundle\Model;
 
/**
 * An interface that the invoice Subject object should implement.
 * In most circumstances, only a single object should implement
 * this interface as the ResolveTargetEntityListener can only
 * change the target to a single object.
 * 这是invoice对象应该实现的接口。
 * 很多时候，只应有一个对象来实现这个接口，
 * 因为ResolveTargetEntityListener只能改变目标到一个对象
 */
interface InvoiceSubjectInterface
{
    // List any additional methods that your InvoiceBundle
    // will need to access on the subject so that you can
    // be sure that you have access to those methods.
    // 列出了每一个附加方法，你的InvoiceBundle需要用这些方法来
    // 访问Subject，这样可以确保你拥有那些方法的访问权
 
    /**
     * @return string
     */
    public function getName();
}