Automapper with EnumMapping throws on nullable Enums with unknown value

Question

I have a nullable enum property on the source side and get this property with value 0 instead of NULL. But 0 is not a represented value in the enum so AutoMapper with ConvertUsingEnumMapping throws an exception that the enum can not be mapped. Is there a way to map it to NULL whenever the value is not represented in the source enum? Some way to prevent this runtime error?

public class SomeSourceDto
{
    public SomeSourceEnum? SomeEnum { get; set; }
}

public class SomeDestinationDto
{
    public SomeDestinationEnum? SomeEnum { get; set; }
}

public enum SomeSourceEnum
{
    First = 1
}

public enum SomeDestinationEnum
{
    First = 1
}

Mapping configuration:

CreateMap<SomeSourceDto, SomeDestinationDto>();
CreateMap<SomeSourceEnum, SomeDestinationEnum>().ConvertUsingEnumMapping(opt => opt.MapByName());

Mapping:

var someSourceDto = new SomeSourceDto { SomeEnum = 0 };
Mapper.Map<SomeDestinationDto>(someSourceDto);

Exception:

AutoMapper.AutoMapperMappingException

Error mapping types.

...

Destination Member:

SomeEnum

My current workaround is to apply this before the map:

someSourceDto.SomeEnum = someSourceDto.SomeEnum == 0 ? null : someSourceDto.SomeEnum;

Is there a better way? I can't use ConvertUsingEnumMapping when I make the enum types in the map nullable.

The problem is that this can happen for every enum property so I'm at big risk of runtime errors atm because I have no control over the source side of the data.

Answer 1

You can work it around like this:

CreateMap<SomeSourceDto, SomeDestinationDto>()
    .ForMember(
        dst => dst.SomeEnum,
        opt => opt.MapFrom(
            src => Enum.IsDefined(typeof(SomeDestinationEnum), src.SomeEnum) 
            ? src.SomeEnum 
            : null));

You can rewrite this to an extension method so you can use it more easily for other DTO's