Default mapping configuration for inherited classes in AutoMapper

Question

Is it possible to create a default destination mapping in AutoMapper ?

Source classes:

class SourceA { 
  public string X { get; set; } 
}
class SourceB { 
  public string Y { get; set; } 
}

Destination classes:

class DestBase { 
  public List<string> Z { get; set; }
}
class DestA : DestBase { 
  public string X { get; set; } 
}
class DestB : DestBase { 
  public string Y { get; set; } 
}

And the mapping configuration contains the following:

cfg.CreateMap<SourceA, DestA>()
  .ForMember(dest => dest.Z, src => src.MapFrom(s => null));
cfg.CreateMap<SourceB, DestB>()
  .ForMember(dest => dest.Z, src => src.MapFrom(s => null));

Is it possible to create a default mapping for all destination classes inheriting the DestBase to avoid the repeated .ForMember(...) lines ?

eg. something like:

cfg.CreateMap<object, DestBase>
   .ForMember(dest => dest.Z, src => src.MapFrom(s => new List<string>()));

Answer 1

In principle yes, with the Include method, but there is a caveat.

If you define a map from source type object , this map would match all types. Maybe you can introduce an interface ISource for the source types that should be affected by this mapping.

So it could look like this:

    class SourceA : ISource { 
        public string X { get; set; } 
    }

    class SourceB : ISource { 
        public string Y { get; set; } 
    }

    cfg.CreateMap<ISource, DestBase>
       .Include<SourceA, DestA>
       .Include<SourceB, DestB>
       .Include<SourceC, DestC>
       .ForMember(dest => dest.Z, , o => o.MapFrom(src => new List<string>()));

    cfg.CreateMap<SourceA, DestA>()
        .ForMember(dest => dest.X, o => o.MapFrom(src => src.X));

    cfg.CreateMap<SourceB, DestB>()
        .ForMember(dest => dest.Y, o => o.MapFrom(src => src.Y));

    // still need to create a map even if no additional properties are to be mapped
    cfg.CreateMap<SourceC, DestC>();

Note that you still need to create maps for all included types, even if there are no additional properties to map.