AutoMapper and inheritance - How to Map?

Have this scenario:

public class Base {  public string Name; }

public Class ClassA :Base {  public int32 Number;  }

public Class ClassB :Base { public string Description;}

public Class DTO {
  public string Name;
  public int32 Number;
  public string Description;
}

I have an IList<Base> my maps are:

AutoMapper.Mapper.CreateMap<IList<Base>, IList<DTO>>()
   .ForMember(dest => dest.Number, opt => opt.Ignore())
   .ForMember(dest => dest.Description, opt => opt.Ignore());

AutoMapper.Mapper.CreateMap<ClassA, DTo>()
   .ForMember(dest => dest.Description, opt => opt.Ignore());

AutoMapper.Mapper.CreateMap<ClassB, DTO>()
   .ForMember(dest => dest.Number, opt => opt.Ignore())

Mapper.AssertConfigurationIsValid(); //Is OK!

But Properties that are in ClassA Or ClassB are not mapped when I do this :

IList<DTO>= AutoMapper.Mapper.Map<IList<Base>,IList<DTO>>(baseList);

How can I do to map properties that are defined in ClasA and ClassB

Solution 1:

You will need to create DTO classes that match your domain classes like this:

public class DTO
{
    public string Name;
}

public class DTO_A : DTO
{
    public int Number { get; set; }
}

public class DTO_B : DTO
{
    public string Description { get; set; }
}

You then need to change your mappings to this:

        Mapper.CreateMap<Base, DTO>()
            .Include<ClassA, DTO_A>()
            .Include<ClassB, DTO_B>();

        Mapper.CreateMap<ClassA, DTO_A>();

        Mapper.CreateMap<ClassB, DTO_B>();

        Mapper.AssertConfigurationIsValid();

Once this is done, then the following will work:

        var baseList = new List<Base>
        {
            new Base {Name = "Base"},
            new ClassA {Name = "ClassA", Number = 1},
            new ClassB {Name = "ClassB", Description = "Desc"},
        };

        var test = Mapper.Map<IList<Base>,IList<DTO>>(baseList);
        Console.WriteLine(test[0].Name);
        Console.WriteLine(test[1].Name);
        Console.WriteLine(((DTO_A)test[1]).Number);
        Console.WriteLine(test[2].Name);
        Console.WriteLine(((DTO_B)test[2]).Description);
        Console.ReadLine();

Unfortunately this does mean that you have an unwanted cast, but I don't think there's much that you can do about that.

Solution 2:

At least with recent Automapper versions (>2.0?) your code is okay if you remove the IList<>:s of your first CreateMap statement¹. And you don't have to create specific DTO classes as @Simon suggests in another answer (unless that's what you want).

But to be specific about the inheritance and to avoid redundant mapping clauses when you extend the base class you can specify the inheritance by using the .Include method. So, if you create your mappings like this:

Mapper.CreateMap<Base, DTO>()
    .Include<ClassA, DTO>()
    .Include<ClassB, DTO>()
    .ForMember(dest => dest.Description, opt => opt.Ignore())
    .ForMember(dest => dest.Number, opt => opt.Ignore());

Mapper.CreateMap<ClassA, DTO>()
    .ForMember(dest => dest.Description, opt => opt.Ignore());

Mapper.CreateMap<ClassB, DTO>()
    .ForMember(dest => dest.Number, opt => opt.Ignore());

Mapper.AssertConfigurationIsValid(); //Is OK!

then you can do this:

var baseList = new List<Base>
{
    new Base {Name = "Base"},
    new ClassA {Name = "ClassA", Number = 1},
    new ClassB {Name = "ClassB", Description = "Desc"},
};

var test = Mapper.Map<IList<Base>, IList<DTO>>(baseList);
Console.WriteLine(test[0].Name);
Console.WriteLine(test[1].Name);
Console.WriteLine((test[1]).Number);
Console.WriteLine(test[2].Name);
Console.WriteLine((test[2]).Description);
Console.ReadLine();

(Note that you don't have to map IList specifically. Automapper handles this for you.)
See this article about .Include.

¹_{Actually I wonder if the code compiled as written in the question?}

Solution 3:

Following on from Eugene Gorbovoy's answer, if you're using profiles to configure your AutoMapper, you need to use a TypeConverter.

Create a new TypeConverter like this

    public class NumberConverter : ITypeConverter<DTO, NumberBase>
    {
        public NumberBase Convert(DTO source, NumberBase destination, ResolutionContext context)
        {
            if (source.Id % 2 == 0)
            {
                return context.Mapper.Map<EvenNumber>(source);
            }
            else
            {
                return context.Mapper.Map<OddNumber>(source);
            }
        }
    }

and replace the ConvertUsing line in his example with

  expression.CreateMap<DTO, NumberBase>()
            .ConvertUsing(new NumberConverter());