AutoMapper cannot convert enum to nullable int?

Question

I got AutoMapperMappingException exception

Exception of type \'AutoMapper.AutoMapperMappingException\' was thrown. ---> System.InvalidCastException: I

Answer 1

It looks like no, it won't take care of this automatically for you. Interestingly, it will map an enum to a regular int.

Looking at AutoMapper's source, I think the problematic line is:

Convert.ChangeType(context.SourceValue, context.DestinationType, null);

Assuming context.SourceValue = DummyTypes.Foo and context.DestinationType is int?, you would end up with:

Convert.ChangeType(DummyTypes.Foo, typeof(int?), null)

which throws a similar exception:

Invalid cast from 'UserQuery+DummyTypes' to 'System.Nullable`1[[System.Int32, mscorlib, Version=4.0.0.0

So I think really the question is why can't we cast a variable of type enum to int? That question has already been asked here.

This seems like a bug in AutoMapper. Anyway the workaround is to map the property manually:

Mapper.CreateMap<DummySource, DummyDestination>()
    .ForMember(dest => dest.Dummy, opt => opt.MapFrom(src => (int?)src.Dummy));

Answer 2

Just in case if anyone want to try using a type converter

Mapper.CreateMap<int?, DummyTypes.Foo?>().ConvertUsing(new FooTypeConverter());

public class FooTypeConverter: TypeConverter<int?, DummyTypes.Foo?>
    {
        protected override DummyTypes.Foo? ConvertCore(int? source)
        {
            return source.HasValue ? (DummyTypes.Foo?)source.Value : null;
        }
    }

Cheers