如何在DTO中映射相关DTO的列表：嵌套DTO映射

Question

Suppose you have a fully defined relationship of books and authors in a large database with many other relationships

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; }
   ...
}

And in your controller you want to return a list of authors, each containing the list of books associated with them using DTOs.

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; }
}

What is the right way to generate that list of DTOs within a DTO?

Could you do something like this?

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()
   };

Or maybe something like this?

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()
    };

EDIT:

To hopefully be a bit clearer, I rephrased and reposed my question here:

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

Answer 1

What I mean is that you can do something as the following:

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 })
        };

For this, instead of declaring Books as List<BookDTO> declare it as IEnumerable<BookDTO> .

Answer 2

You can do this using AutoMapper . You don't need to repeat yourself everywhere. You'll need to add Profile so the mapping will work each time you caller the IMapper.Map function.

See this example

  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));
          }
     }
  }

now in your controllers you need to inject IMapper to be able to use IMapper.Map<TSource, TDestination> method.

     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 3

This is Mapper profile example. Profile class comes from Automapper lib.

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());
    }
}

This is How you can map.GetAuthors Method returns mapped 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);
    }
}