应用服务组合 [英] Application Services Composition

问题描述

我有一个客户实体，该实体具有到城市的推荐人：

I've a Customer entity that has an referente to City:

public class Customer
{
    public int CustomerId { get; set; }

    public int CityId { get; set;}
}

然后，提供以下应用程序服务：

Then, the following application service:

public class CustomerService
{
    private readonly ICustomerRepository customerRepository;

    public CustomerService(ICustomerRepository customerRepository)
    {
        this.customerRepository = customerRepository;
    }

    public void RegisterCustomer(Customer customer)
    {
        //Do another things...

        customerRepository.Save(customer);
    }
}

要注册新客户，服务消费者必须可以访问要放入CityId的城市列表，例如获取要填充组合框的城市列表。

To register a new customer the service consumer would have to have access to a listing of cities to put in CityId, such as get the list of cities to fill a combobox.

因此，有必要提供列表城市操作。

Thus it would be necessary provide a list city operation.

我应该将此操作添加到CustomerService吗？

Should i add this operation to CustomerService?

就像：

public class CustomerService
{
    private readonly ICustomerRepository customerRepository;
    private readonly ICityRepository cityRepository;

    public ServicoCliente(
        ICustomerRepository customerRepository, 
        ICityRepository cityRepository)
    {
        this.customerRepository= customerRepository;
        this.cityRepository= cityRepository;
    }

    public void RegisterCustomer(Customer customer)
    {
        customerRepository.Save(customer);
    }

    public List<City> ListCities()
    {
        return cityRepository.GetAll();
    }
}

或创建新服务：

public class CityService
{
    private readonly ICityRepository cityRepository;

    public CityService(ICityRepository cityRepository)
    {
        this.cityRepository= cityRepository;
    }

    public List<City> ListCities()
    {
        return cityRepository.GetAll();
    }
}

在后一种情况下，消费者应该引用两项服务才能完成一项操作：RegisterCustomer。

In the latter case the consumer should have references two services to be able to complete one operation: RegisterCustomer.

采用哪种方法？

推荐答案

这是一个代码组织问题，与DDD无关。

This is a code organization issue and has little to do with DDD.

公共类客户服务{

公共列表列表城市（）
{
return cityRepository.GetAll（）;
}

public List ListCities() { return cityRepository.GetAll(); }

}

这里有明显的不匹配- -您不希望通过客户服务公共界面方法返回城市。这打破了最不令人惊讶的原则，并会引起很多搜索和开发者的不满。

There's an obvious mismatch here -- you don't expect from a Customer service public interface method to return cities. This breaks the principle of least surprise and will cause a lot of searching and head scratching for generations of developers to come.

专用服务对我来说似乎是个好主意。

A dedicated service seems like a better idea to me.

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