automapper map interface to interface or object

Question

How to map objects inherited from one interface to objects inherited from another interface.

I have such code structure

public interface IDataTranslatable
{
    List<DataTranslation> SpanishDataTranslations {get;set;}
}

public interface IDataTranslatableDto
{
    List<DataTranslationDto> DataTranslations { get; set; }
}

objects DataTranslation and DataTranslationDto have the same properties. I have many objects inherited from IDataTranslatable and IDataTranslatableDto interfaces. For example

public class Category : IDataTranslatable
{
    public string Name { get; set; }
    public ICollection<DataTranslation> SpanishDataTranslations { get; set; } = new List<DataTranslation>();
}

public class CategoryDto : IDataTranslatableDto
{
    public string Name { get; set; }
    public List<DataTranslationDto> DataTranslations { get; set; } = new List<DataTranslationDto>();
}

The best implementation for me would be something like that

config.CreateMap<IDataTranslatable, IDataTranslatableDto>()
.ForMember(dest => dest.DataTranslations, opts => opts.MapFrom(src => src.SpanishDataTranslations));

By this I mean that any object inherited from IDataTranslatable has to be mapped to object inherited IDataTranslatableDto to corresponding fields.

But this won't work, So I've tried to map like that

config.CreateMap<IDataTranslatable, CategoryDto>()
.ForMember(dest => dest.DataTranslations, opts => opts.MapFrom(src => src.SpanishDataTranslations));

Current using

public class AutoMapperConfiguration : IAutoMapperConfiguration
{
    public void Configure(IMapperConfigurationExpression config)
    {
        IDataTranslatableMappings(config);
    }

    private void IDataTranslatableMappings(IMapperConfigurationExpression config)
    {
        var mapCategory = config.CreateMap<Category, CategoryDto>().ForMember(dest => dest.DataTranslations, opts => opts.MapFrom(src => src.SpanishDataTranslations));
    }
}

This variant doesn't work as well. I've tried to explain my idea, how would be better to do it?

Answer 1

You can configure it the following way:

Mapper.Initialize(config =>
{
    config.CreateMap<IDataTranslatable, IDataTranslatableDto>()
                .ForMember(x => x.DataTranslations, y => y.MapFrom(src => src.SpanishDataTranslations));
                
    config.CreateMap<Category, CategoryDto>()
                .IncludeBase<IDataTranslatable, IDataTranslatableDto>();                    

    config.CreateMap<DataTranslation, DataTranslationDto>();
});

And the usage of it:

var translation = new DataTranslation()
{
    Test = "Foo"
};

IDataTranslatable category = new Category()
{
     SpanishDataTranslations = new List<DataTranslation> { translation }
};

var result = Mapper.Map<IDataTranslatableDto>(category);

You will be forced to add every implementation of IDataTranslatable and IDataTranslatableDto to the mapping configuration.

---

Update

From version 8.0 and above, you can use IncludeDerived on your base type and therefore no longer need to explicitly declare all implementations of your interface.