Automapper：映射列表到 object

Question

Im having problems mapping my domain to my DTO.

The error is: Expression must resolve to top-level member and not any child object's properties. You can use ForPath, a custom resolver on the child type or the AfterMap option instead.

public class Sign
{
   public List<Item> Items { get; set; } = new List<Item>();
}
        
public class SignDTO
{
   public SignItemDTO Items { get; set; } = new SignItemDTO();
}
        
public class SignItemDTO
{
  public List<ItemDTO> Items { get; set; } = new List<ItemDTO>();
}

    private MapperConfiguration AutoMapperConfig()
    {
      return new MapperConfiguration(cfg =>
          {
     cfg.CreateMap<Item, ItemDTO>();
          cfg.CreateMap<Sign, SignDTO>().ForPath(dest => dest.Items.Items, opt => opt.MapFrom(src => src.Items));
                });
            }

_context.Sign.Include(m => m.Items)
.ProjectTo<SignDTO>(AutoMapperConfig());

Answer 1

Probably it's due to your map in this line:

cfg.CreateMap<Sign, SignDTO>().ForPath(dest => dest.**Items.Items**, opt => opt.MapFrom(src => src.**Items**));

As you can see in between the **, you're maping from an entity property to another entity children's property, this is what AutoMapper does not like and what you see in the error message.

Maybe it was a mistake on your side an you can removed one of the Items or you can create a new mapping for your first level of Items which takes care of the childrens.