DTO是否应置于其作用的类内部？中等开发者技术问询

Hey Alan, nice to see you digging into DTO patterns and experimenting with different structures—let’s talk through your approach and other common options that might fit your workflow.

你的嵌套DTO写法完全可行（甚至推荐中小型项目） #

First off, embedding DTOs inside their corresponding domain classes (like you’ve already tried) is a totally valid approach, and one that many developers prefer for smaller to mid-sized projects. Here’s a quick example to mirror what you’ve probably written:

public class Order
{
    public int OrderId { get; set; }
    public DateTime OrderDate { get; set; }
    public List<OrderItem> Items { get; set; }

    // 嵌套的DTO类，和Order强关联
    public class OrderDto
    {
        public int OrderId { get; set; }
        public DateTime OrderDate { get; set; }
        public int TotalItems { get; set; }
        public decimal TotalAmount { get; set; }
    }
}

This setup has some great perks:

• Intuitive organization: Anyone reading the Order class immediately sees what data gets exposed via the DTO, no need to hunt through separate folders.
• No naming collisions: You don’t have to worry about generic names like OrderDto clashing with similar classes from other domains (since it’s scoped to Order.OrderDto).
• Easy maintenance: When you update the Order domain model, you can tweak the nested DTO right alongside it without jumping between files.

其他常见的存放方案（适合不同场景） #

If your project grows or you need more flexibility, here are two other standard patterns:

• Separate DTO folder/class library
  For larger applications where DTOs are reused across multiple layers (e.g., API, services, client apps), create a dedicated Dtos folder (or even a standalone class library like YourApp.Core.Dtos). You can group DTOs by domain to keep things organized:

  /Dtos
    /Orders
      OrderDto.cs
      OrderItemDto.cs
    /Users
      UserProfileDto.cs
      UserLoginDto.cs
  

  This works well if you want to decouple your domain models from the data you expose externally.

• API-layer specific DTOs
  If your DTOs are only used to shape API responses/requests, keep them right alongside your controllers. For example, in an ASP.NET Core project:

  /Controllers
    OrdersController.cs
    /Dtos
      OrderRequestDto.cs
      OrderResponseDto.cs
  

  This keeps your API logic self-contained—when you modify an endpoint, you can adjust the DTO in the same context.

Quick note on AutoMapper #

Even though you haven’t integrated AutoMapper yet, your nested DTO approach plays nicely with it. When you do set it up, mapping is straightforward:

// 配置映射
CreateMap<Order, Order.OrderDto>()
    .ForMember(dest => dest.TotalItems, opt => opt.MapFrom(src => src.Items.Count))
    .ForMember(dest => dest.TotalAmount, opt => opt.MapFrom(src => src.Items.Sum(i => i.Price)));

Final takeaway #

There’s no one-size-fits-all answer, but your current nested structure is a solid choice for your skill level and likely project size. It keeps things simple and cohesive. As your project scales, you can always refactor to a separate folder/library if needed.

内容的提问来源于stack exchange，提问作者Alan