Map a 2nd level nested list property to first level list property with automapper

Question

I need your help. I have basic experience with automapper and it all works great, but in one way or another i can't map my next change in the source object to my destination object.

Let me explain it a bit:
In IUser, i added a property 'UserDetails' and this class contains a List of Guid property called 'Domains'.

I want to map that second level list property to my UserDto object where the list of guid property is at first level. In the example below, the Userkey mapping works fine, but i keep getting null for 'DomainIds' and don't see what i'm doing wrong. I Hope you can help me

public interface IUser
{
    UserKey Key { get; }
    UserDetails Details { get; set; }
    FirstName { get; }
}

public struct UserKey
{
    private readonly Guid _id;
    public UserKey(Guid id)
    {
        _id = id;
    }
}

public class UserDetails
{
    public List<Guid> Domains { get; set; }
}

public class UserDto
{
    public Guid Id { get; set; }
    public string FirstName { get; set; }
    public List<Guid> DomainIds { get; set; }
}

The mapping setup is the following:

CreateMap<IUser, UserDto>()
            .ForMember(
                dest => dest.Id,
                opt => opt.MapFrom(src => src.Key.Id))
            .ForMember(
                dest => dest.DomainIds,
                opt => opt.MapFrom(src => src.Details.Domains))

In my test i map user (which is an IUser) like this. Fyi, all other properties are mapping fine

_mapper.Map<UserDto>(user);

I never use AutoMapper for non-trivial mappings. Some `FromDto` and `ToDto` [extension] methods are just simpler, faster, easier to debug and more sensitive to code changes. Mapping between different class layouts results in practically as much code (or even more with tons of lambdas) as simply writing the mapping manually. See also: https://cezarypiatek.github.io/post/why-i-dont-use-automapper/ — György Kőszeg, Dec 15 '18 at 09:57
If you can change the names, you can get a cleaner mapping using the default [flattening](http://docs.automapper.org/en/latest/Flattening.html). — Lucian Bargaoanu, Dec 15 '18 at 11:00
@taffer Thanks. I read the blog post and it has some good reasons. I removed automapper and created my own mappers. all is working fine now. — mkeymolen, Dec 15 '18 at 20:45

score 0 · Answer 1 · answered Dec 15 '18 at 10:33

Your mapping appears to work fine for me:

Mapper.Initialize(config =>
{
    config.CreateMap<User, UserDto>()
        .ForMember(
            dest => dest.Id,
            opt => opt.MapFrom(src => src.Key.Id))
        .ForMember(
            dest => dest.DomainIds,
            opt => opt.MapFrom(src => src.Details.Domains));
});

var user = new User
{
    FirstName = "foo",
    Key = new UserKey { Id = Guid.NewGuid() },
    Details = new UserDetails
    {
        Domains = new List<Guid> { Guid.NewGuid(), Guid.NewGuid(), Guid.NewGuid() },
    },
};

var result = Mapper.Map<UserDto>(user);

Using the following types:

public class User
{
    public UserKey Key { get; set; }
    public UserDetails Details { get; set; }
    public string FirstName { get; set; }
}
public class UserKey
{
    public Guid Id {get;set;}
}
public class UserDetails
{
    public List<Guid> Domains { get; set; }
}

public class UserDto
{
    public Guid Id { get; set; }
    public string FirstName { get; set; }
    public List<Guid> DomainIds { get; set; }
}

Map a 2nd level nested list property to first level list property with automapper

1 Answers1