如何在 DTO 中映射相关 DTO 列表：嵌套 DTO 映射

Question

假设您在大型数据库中具有完全定义的书籍和作者关系以及许多其他关系

public class Book
{
   public int Id { get; set; }
   public string Title { get; set; }
   ...
   Public int AuthorId { get; set; }
   Public Author Author { get; set; }
}

public class Author
{
   public int Id { get; set; }
   public int GroupId { get; set; }
   public string Name { get; set; }
   ...
   public List<Book> Books { get; set; }
   ...
}

在您的控制器中，您希望返回一个作者列表，每个作者都包含使用 DTO 与他们关联的书籍列表。

public class BookDTO
{
   public int Id { get; set; }
   public string Title { get; set; }
}

public class AuthorDTO
{
   public int Id { get; set; }
   public string Name { get; set; }
   public List<BookDTO> Books { get; set; }
}

在 DTO 中生成 DTO 列表的正确方法是什么？

你能做这样的事吗？

var author = from a in _context.authors.Where(a => a.groupId == someGroup)
   select new AuthorDTO()
   {
      Id = a.Id,
      Name = a.Name,
      Books = (from b in a.Books
         select new BookDTO()
         {
            Id = b.Id,
            Title = b.Title
         }).ToList()
   };

或者可能是这样的？

var author = from a in _context.authors.Where(a => a.groupId == someGroup)
   select new AuthorDTO()
   {
      Id = a.Id,
      Name = a.Name,
      Books = (from b in _context.books.Where(b => b.AuthorId == a.AuthorId)
         select new BookDTO()
         {
            Id = b.Id,
            Title = b.Title
         }).ToList()
    };

编辑：

为了更清楚一点，我在这里重新表述并提出了我的问题：

How to return list of DTO with nested lists of related DTO

Answer 1

您可以使用AutoMapper 执行此操作。你不需要到处重复自己。 您需要添加Profile，以便每次调用IMapper.Map 函数时映射都会起作用。

看这个例子

  public class BookDTO
  {
     public int Id { get; set; }
     public string Title { get; set; }

     public class MapProfile:AutoMapper.Profile{
          public MapProfile(){
              CreateMap<Book,BookDTO>().ReverseMap();
          }
     }
  }

  public class AuthorDTO
  {
     public int Id { get; set; }
     public string Name { get; set; }
     public List<BookDTO> Books { get; set; }


     public class MapProfile:AutoMapper.Profile{
          public MapProfile(){
              CreateMap<Author,AuthorDTO>()
              .ForMember(dest.Id, opt => opt.MapFrom(src.Id))
              .ForMember(dest.Name, opt => opt.MapFrom(src.Name))
              .ForMember(dest.Books, opt => opt.MapFrom(src.Books));
          }
     }
  }

现在您需要在控制器中注入 IMapper 才能使用 IMapper.Map<TSource, TDestination> 方法。

     public class AuthorController : Controller{

         private readonly IMapper mapper;
         private readonly Context context;

           public AuthorController(IMapper mapper, Context context){
                 mapper =mapper;
                //...context=context;
           }
           public IActionResult Index(){
              var authors = context.Author.Include(a=>a.Book).ToList();
             var authorDTOs = mapper.Map<List<AuthorDTO>>(authors);
             return View(authorDTOs);
           }
     }

Answer 2

这是 Mapper 配置文件示例。 Profile 类来自 Automapper 库。

public class ApplicationServiceAutoMapperProfile : Profile
{
    public ApplicationServiceAutoMapperProfile()
    {
         //Don't use ForMember method if you want to show Id's
         CreateMap<Book, BookDTO>()
            .ForMember(m => m.Id, opt => opt.Ignore());

         CreateMap<Author, AuthorDTO>()
            .ForMember(m => m.Id, opt => opt.Ignore());
    }
}

这就是你可以如何 map.GetAuthors 方法返回映射的 Dtos。

public class CustomService {
    private readonly IMapper _mapper;
    private readonly DBContext _context;

    public CustomService(IMapper mapper, DBContext context){
        _mapper = mapper;
        _context = context;
    }

    public IEnumerable<AuthorDTO> GetAuthors(){
        //Automapper automaticaly maps authors's bookdto's also.
        var authors = _context.authors.Where(a => a.groupId == 2).ToList();
        return _mapper.Map<List<AuthorDTO>>(authors);
    }
}

Answer 3

我的意思是您可以执行以下操作：

var q = from b in Books
        group b by b.Author into g
        select new AuthorDTO 
        { 
           Name = g.Key.Name, 
           Books = g.Select(gi => new BookDTO { Title = gi.Title })
        };

为此，不要将Books 声明为List<BookDTO>，而是将其声明为IEnumerable<BookDTO>。