如何在DTO中映射相关DTO的列表：嵌套DTO映射

Question

假设您在大型数据库中拥有书籍和作者的完全定义的关系，还有许多其他关系

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; }
   ...
}

并且在您的控制器中，您想返回一个作者列表，每个作者都包含使用DTO与他们相关联的书籍的列表。

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？

你能做这样的事情吗？

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()
   };

或者也许是这样？

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，我在这里改写并提出了我的问题：

如何使用相关DTO的嵌套列表返回DTO列表

Answer 1

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> 。

Answer 2

您可以使用AutoMapper进行此操作。 您无需到处重复。 您将需要添加Profile以便每次调用IMapper.Map函数时映射都将起作用。

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，在您的控制器中，您需要注入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 3

这是Mapper配置文件示例。 配置文件类来自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());
    }
}

这就是映射方法。GetAuthors方法返回映射的Dto。

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);
    }
}