Can AutoMapper implicitly flatten this mapping? - automapper

Question

I am trying to map between two lists of objects. The source type has a complex property of type A; the destination type is a flattened subset of type A plus an additional scalar property that is in the source type.
public class A
{
public int Id { get; set; }
public string Name { get; set; }
}
public class Source
{
public A MyA { get; set; }
public int SomeOtherValue { get; set; }
}
public class Destination
{
public string Name { get; set; }
public int SomeOtherValue { get; set; }
}
If it's not clear, I'd like Source.MyA.Name to map to Destination.Name and Source.SomeOtherValue to map to Destination.SomeOtherValue.
In reality, type A has a dozen or so properties, about which 80% map over to properties of the same name in Destination. I can get things to work if I explicitly spell out the mappings in CreateMap like so:
CreateMap<Source, Destination>()
.ForMember(dest => dest.Name, opt => opt.MapFrom(src => src.MyA.Name));
The downside here is I want to avoid having to add a ForMember line for each of A's properties that need to get copied over to Destination. I was hoping I could do something like:
CreateMap<Source, Destination>()
.ForMember(dest => dest, opt => opt.MapFrom(src => src.MyA));
But if I try the above I get a runtime error when the mapping is registered: "Custom configuration for members is only supported for top-level individual members on a type."
Thanks

Answer 1

create mappings between A and Destination, and Source and Destination, and then use AfterMap() to use first mapping in second
Mapper.CreateMap<A, Destination>();
Mapper.CreateMap<Source, Destination>()
.AfterMap((s, d) => Mapper.Map<A, Destination>(s.MyA, d));
then use it like this:
var res = Mapper.Map<Source, Destination>(new Source { SomeOtherValue = 7, MyA = new A { Id = 1, Name = "SomeName" } });

Answer 2

As a workaround you can use custom type converter with additional property in the destination type to avoid recursion.
[TestFixture]
public class MapComplexType
{
[Test]
public void Map()
{
Mapper.CreateMap<A, Destination>();
Mapper.CreateMap<Source, Destination>().ConvertUsing(new TypeConvertor());
var source = new Source
{
MyA = new A
{
Name = "Name"
},
SomeOtherValue = 5
};
var dest = new Destination();
Mapper.Map(source, dest);
Assert.AreEqual(dest.Name, "Name");
}
}
public class TypeConvertor : ITypeConverter<Source, Destination>
{
public Destination Convert(ResolutionContext context)
{
var destination = (Destination) context.DestinationValue;
if (!((Destination)context.DestinationValue).IsMapped || destination == null)
{
destination = destination ?? new Destination();
destination.IsMapped = true; // To avoid recursion
Mapper.Map((Source)context.SourceValue, destination);
destination.IsMapped = false; // If you want to map the same object few times
}
Mapper.Map(((Source)context.SourceValue).MyA, destination);
return (Destination)context.DestinationValue;
}
}
public class A
{
public int Id { get; set; }
public string Name { get; set; }
}
public class Source
{
public A MyA { get; set; }
public int SomeOtherValue { get; set; }
}
public class Destination
{
public string Name { get; set; }
public int SomeOtherValue { get; set; }
// Used only for mapping purposes
internal bool IsMapped { get; set; }
}

Answer 3

Try this,
Mapper.CreateMap<A, Destination>();
Mapper.CreateMap<Source, Destination>()
.ForMember(destination => destination.Name, options => options.MapFrom(source => Mapper.Map<A, Destination>(source.MyA).Name));
var objSource = new Source { SomeOtherValue = 7, MyA = new A { Id = 1, Name = "SomeName" } };
var result = Mapper.Map<Source, Destination>(objSource);