使用AutoMapper使用派生对象而不是父对象的映射

Question

I can't figure a solution to my problem using AutoMapper nor find right keywords to find a solution online, hence the maybe bad title for that question, here is my problem:

I'd like to force AutoMapper to use one map out of two valid maps. Here an exemple:

public class A
{
    public B B { get; set; }
}

public class ADTO
{
    public BDTO B { get; set; }
}

public class B
{
}

public class BDTO
{
}

public class CDTO : BDTO
{
}

public class AProfile : Profile
{
    public AProfile()
    {
        Mapper.CreateMap<B, BDTO>();
        Mapper.CreateMap<B, CDTO>();

        // Is there a way to force AutoMapper to use B to CDTO instead of B to BDTO ?
        Mapper.CreateMap<A, ADTO>()
            .ForMember(adto => adto.B, opt => opt.MapFrom(a => a.B));
    }
}

If I remove below line, AutoMapper throws an error saying that it can't find a valid map for B property in A to ADTO map.

Mapper.CreateMap<B, BDTO>();

Is there any way to make my map B to CDTO valid for it ?

EDIT from Lucian answer

So I guess one solution is to make it two steps :

var a = new A { B = new B() }
var adto = new ADTO();

adto = Mapper.Map(a, adto); // Map B to BDTO
adto.B = Mapper.Map<CDTO>(a.B); // Change BDTO to CDTO

I'm more into one proper line solution :

var a = new A { B = new B() }
var adto = new ADTO();

adto = Mapper.Map(a, adto); // Map directly B to CDTO

Any way to make it happen ?

EDIT 2 from Lucian answer again

The fact is that A and B are entities coming from EF and that I don't have access to ADTO initialization as I use .ProjectTo extension.

My code is something more like:

var adto = db.As.ProjectTo<ADTO>().ToList();

Where db is my DbContext and As my DbSet of A .

EDIT 3 from Lucian answer again

I did not know about that ConstructProjectionUsing method, thanks for that! Here the code I manage to build with your answer.

Mapper.CreateMap<A, ADTO>()
   .ConstructProjectionUsing(a => new ADTO() { B = new CDTO() })
   .ForMember(adto => adto.B, opt => opt.MapFrom(a => a.B));

And that's brillant! But now, I have another problem, B and BDTO are in fact ICollection and IEnumerable... I didn't think it will be a problem so I didn't tell. Here the updated code:

public class A
{
    public ICollection<B> B { get; set; }
}

public class ADTO
{
    public IEnumerable<BDTO> B { get; set; }
}

So I think I can't use the ConstructProjectionUsing as this code won't compile:

Mapper.CreateMap<A, ADTO>()
   .ConstructProjectionUsing(a => new ADTO() { B = new List<CDTO>() }) // Error here, can't convert List<CDTO> to List<BDTO> 
   .ForMember(adto => adto.B, opt => opt.MapFrom(a => a.B));

I guess I'm stuck here ?

Answer 1

You can initialize ADTO.B with an instance of CDTO and map to an existing object.

var a = new A { B = new B() };  
var adto = new ADTO { B = new CDTO() };  
Mapper.Map(a, adto); // Map directly B to CDTO

This would work with a newer AM. You might need UseDestinationValue with older ones.

Answer 2

For construction you can use ConstructProjectionUsing. An example . But otherwise, I think you need the right type in the destination.

Answer 3

OK, so As is what allows you to redirect the map. And it seems to work with ProjectTo. See here .

 Mapper.CreateMap<B, BDTO>().As<CDTO>();

Of course this applies everywhere, not only for ProjectTo.