Manual mapping with extension methods

#Mapping with Extension Methods.cs

public static class OrderMappingsExtensions
{
	public static void Fill(this FaithfulOrderDto target, Order source)
	{
		target.Total = source.Total;
		target.Customer = MapTo<CustomerDto>().From(c => c.Fill(source.Customer));
		
		// Additionally, we also should have some syntax for ignoring properties
		// to allow a generic test that automatically discovers all Fill methods
		// know which properties are deliberately ignored. Not sure which syntax
		// I'd prefer.
		
		// A Nicest and probably doable, but slightly magical
		// Ignore(target.IgnoredProperty);
		
		// B More basic and also ok
		// Ignore(nameof(FaithfulOrderDto.IgnoredProperty));
		
		// C Less text but too much into the AutoMapper direction?
		// Ignore(() => target.IgnoredProperty);
	}
}

public static class CustomerMappingsExtensions
{
	public static void Fill(this CustomerDto target, Customer source)
	{
		target.Name = source.Name;
	}
}

2_InfrastructureHelpers.cs

public static class MappingExtensions
{
	public class Helper<TTarget>
		where TTarget : new()
	{
		public TTarget From(Action<TTarget> fill)
		{
			var target = new TTarget();
			fill(target);
			return target;
		}
	}

	public static Helper<TTarget> MapTo<TTarget>()
		where TTarget : new()
	{
		return new Helper<TTarget>();
	}
}

3_SampleModel.cs

public class Order
{
	public decimal Total { get; set; }
	public Customer? Customer { get; set; }
}

public class Customer
{
	public string? Name { get; set; }
}

public class FlatOrderDto
{
	public decimal Total { get; set; }
	public string? CustomerName { get; set; }
}

public class CustomerDto
{
	public string? Name { get; set; }
}

public class FaithfulOrderDto
{
	public decimal Total { get; set; }
	public CustomerDto? Customer { get; set; }
}