Service Injection

You will be able to retrieve services from your maps, this could allow you to query objects from the database or from external APIs for example.

public class MyMaps :
    INewMap<Product, ProductDto>,
    IMergeMap<Category, CategoryDto>
{
    ProductDto? INewMap<Product, ProductDto>.Map(Product? source, MappingContext context){
        if(source == null)
            return null;
        else{
            var product = context.ServiceProvider.GetRequiredService<MyDatabase>().Find<Product>(source.Code);

            return new ProductDto{
                Code = source.Code,
                Name = product.Name,
                ...
            };
        }
    }

    CategoryDto? IMergeMap<Category, CategoryDto>.Map(Category? source, CategoryDto? destination, MappingContext context){
        if(source != null){
            var category = context.ServiceProvider.GetRequiredService<MyAPI>().GetCategoryParent(source.Id);

            destination ??= new CategoryDto();
            destination.Id = source.Id;
            destination.Parent = category?.Id;
            ...
        }
        return destination;
    }
}