Automapper automatically resolve correct subclass to map to?

Question

Given the following source types:

public class BaseViewModel
{
   public string Prop1 { get; set; }
}

public class FirstViewModelImpl : BaseViewModel
{
   public string Prop2 { get; set; } 
}

public class SecondViewModelImpl : BaseViewModel
{
   public string AnotherProp { get; set; }
}

And the following destination types

public class BaseDto
{
   public string Prop1 { get; set; }
}

public class FirstDtoImpl : BaseDto
{
   public string Prop2 { get; set; } 
}

public class SecondDtoImpl : BaseViewModel
{
   public string AnotherProp { get; set; }
}

With the following mappings:

Mapper.CreateMap<FirstViewModelImpl,FirstDtoImpl>();
Mapper.CreateMap<SecondViewModelImpl,SecondDtoImpl>();

Can I do the following (trivial example) - given that I don't actually know the type of viewmodel until runtime?

BaseViewModel myViewModel = GetAViewModelFromSomewhere();
FirstDtoImpl dto = (FirstDtoImpl)Mapper.Map<BaseViewModel,BaseDto>(myViewModel);

I am trying this out now anyway!

Answer 1

You can't do that directly, however you can work around it with a TypeConverter.

In the Mappings you will add:

Mapper.CreateMap<BaseViewModel, BaseDto>()
    .ConvertUsing<MyTypeConverter>();

Then you can create the converter like so:

public class MyTypeConverter : TypeConverter<BaseViewModel, BaseDto>
{
    protected override BaseDto ConvertCore(BaseViewModel tViewModel)
    {
        BaseDto vResult = null;
        if(tViewModel is FirstViewModelImpl)
        {
            var vSource = tViewModel as FirstViewModelImpl;
            vResult = Mapper.Map<FirstViewModelImpl,FirstDtoImpl>(vSource);
        }
        else if(tViewModel is SecondViewModelImpl )
        {
            var vSource = tViewModel as SecondViewModelImpl ;
            vResult = Mapper.Map<SecondViewModelImpl ,SecondDtoImpl>(vSource);
        }
        return vResult;
    }
}

Then you can use it like:

BaseDto dto= Mapper.Map<BaseViewModel,BaseDto>(myViewModel);

and have dto actually be of the type you wanted.

It won't map the Base types to each other though. If that matters I can twist it a bit more.

Answer 2

I have found that if I change the mappings to

Mapper.CreateMap<BaseViewModel,BaseDto>()
        .Include<FirstViewModelImpl,FirstDtoImpl>()
        .Include<SecondViewModelImpl,SecondDtoImpl>();

Mapper.CreateMap<FirstViewModelImpl,FirstDtoImpl>();
Mapper.CreateMap<SecondViewModelImpl,SecondDtoImpl>();

Then it works as expected without using the type converter.