Generic Existing Object Mapping

[SunnyVachhetA]

Is your feature request related to a problem? Please describe.
I am trying to map existing object from DTO to Model in Entity Framework Core. It works for normal case by declaring void method as described in Existing Object Mapping.

In below code snippet it gives me error of - RMG001 A mapping method has an unsupported signature.

Describe the solution you'd like
API for updating directly working on existing object with Generic Mapping described in https://mapperly.riok.app/docs/configuration/generic-mapping/.

// Relevant new / adjusted API surface
// Expected generated code

[Mapper]
public partial class CarMapper
{
    public partial void Map<TDestination, TDestination>(TSource source, TDestination destination);
    public partial CarDto CarToCarDto(Car car);
    public partial Car CarDtoToCar(CarDto carDto);
}

Describe alternatives you've considered
I have tried with mentioning return type. But it gives error of method must have an implementation.

[latonz]

How would you implement this method manually?

[SunnyVachhetA]

How would you implement this method manually?

For non-generic, It uses the existing object for mapping without creating new one.

Following that I can think of using the same instance of TDestination passed for mapping source entity.

TSource may or may not have properties that are available in TDestination. Some property values available in TDestination should not be override null by TSource.

I am thinking by above approach. Please note that I am learning about source generator, and I may have unexplored areas in this section.

[latonz]

My question is not really related to source generators. Instead I‘m interested in how you would implement this method manually, without any source generator support.

but I think i understood you wrong, you are not referring to queryable projection mappings correct?
then this looks like a duplicate of #884

[SunnyVachhetA]

Yes @latonz, I was not referring to queryable projection. Generic existing object mapping for class or records only.

Without source generator, I will create a method that takes a existing destination object reference and second one DTO or other object, map them and return the same destination object reference.

[ste4net]

This was exactly what i was searching for... i reach this page from the RMG001 error and with this post i understand it it not possible to do what i was trying to do.
Just to add additional information i was searching for something like this.

public static partial void Map<Tsrc, Ttar>(Tsrc source, Ttar destination);
public static partial void CarToCarDto(Car src, CarDto target);
public static partial void CarDtoToCar(CarDto src, Car target);

with generated code..

   public static void Map<Tsrc, Ttar>(Tsrc source, Ttar targ)
   {
       Type targetType = typeof(Ttar);
       switch (source)
       {
           case Car c when targetType.IsAssignableFrom(typeof(CarDto)):
               CarToCarDto(source as Car, targ as CarDto);
               break;
           case CarDto c when targetType.IsAssignableFrom(typeof(Car)):
               CarDtoToCar(source as CarDto,targ as Car);
               break;
       };
   }