AutoMapper: Problem with mapping records type

Question

I am mapping with automapper 10.1.1 in c# 9 from this class

public record BFrom 
{
    public Guid Id { get; init; }
    public Guid DbExtraId { get; init; }
}

into this

public record ATo(Guid Id, Guid ExtraId) : BaseTo(Id);

And have the following configuration

CreateMap<BFrom, ATo>()
    .ForMember("ExtraId", opt => opt.MapFrom(src => src.DbExtraId))
    .ReverseMap();

But I have a problem when I am trying to map it throws an exception with a message that needs to have a constructor with 0 args or only optional args. Is it possible to fix this problem without changing the record types?

Answer 1

What you need, is to specify the constructor-parameter by name in your mapping profile like so public AToProfile() => CreateMap<BFrom, ATo>().ForCtorParam(ctorParamName: "ExtraId", m => m.MapFrom(s => s.DbExtraId)).ReverseMap(); That way, AutoMapper will know, from where the value should be taken and will map accordingly.

public class StackoverflowQuestionTest
{
    [Fact]
    public void BFrom_MapTo_ATo()
    {
        // Arrange
        IConfigurationProvider configuration = new MapperConfiguration(cfg => cfg.AddProfile<AToProfile>());
        var source = new BFrom {Id = Guid.NewGuid()};

        // Act
        var target = new Mapper(configuration).Map<ATo>(source);

        // Assert
        target.Id.Should().Be(source.Id);
    }


}

public record BaseTo (Guid Id); // this is an assumption, as you did not specify BaseTo in you question

public record BFrom
{
    public Guid Id { get; init; }
    public Guid DbExtraId { get; init; }
}

public record ATo(Guid Id, Guid ExtraId) : BaseTo(Id);

public class AToProfile : Profile
{
    public AToProfile() =>
        CreateMap<BFrom, ATo>()
            .ForCtorParam(ctorParamName: "ExtraId", m => m.MapFrom(s => s.DbExtraId))
            .ReverseMap();
}

Answer 2

I had the same issue, and ended up creating this extension method to solve it:

public static class AutoMapperExtensions
{
    public static IMappingExpression<TSource, TDestination> MapRecordMember<TSource, TDestination, TMember>(
        this IMappingExpression<TSource, TDestination> mappingExpression,
        Expression<Func<TDestination, TMember>> destinationMember, Expression<Func<TSource, TMember>> sourceMember)
    {
        var memberInfo = ReflectionHelper.FindProperty(destinationMember);
        string memberName = memberInfo.Name;
        return mappingExpression
            .ForMember(destinationMember, opt => opt.MapFrom(sourceMember))
            .ForCtorParam(memberName, opt => opt.MapFrom(sourceMember));
    }
}

Then you simply use it like this:

CreateMap<BFrom, ATo>()
    .MapRecordMember(a => a.ExtraId, src => src.DbExtraId)
    .ReverseMap();

and it will take care of registering both constructor and member so that you don't run into issues like these.

Answer 3

Try

CreateMap<BFrom, ATo>().DisableCtorValidation()
    .ForMember("ExtraId", opt => opt.MapFrom(src => src.DbExtraId))
    .ReverseMap()