using System;

using System.Collections.Generic;

using System.Net.Http;

using System.Text.RegularExpressions;

using System.Threading.Tasks;

using AutoMapper;

public class Program

{

    public static void Main()

    {

        var config = new MapperConfiguration(cfg => {

                                                            cfg.CreateMap<Child1, Child2>();

                                                            cfg.CreateMap<Parent, Child2>().ConstructUsing((src, ctx) => ctx.Mapper.Map<Child2>(src.Child1));

                                                            });

        var mapper = config.CreateMapper();

        var parent = new Parent{

            Id = 1,

            Child1 = new Child1 {

                Id = 2

            }

        };

        var child2 = mapper.Map<Parent, Child2>(parent);

        Console.WriteLine(child2.Id); // Returns 1. Expect this to be 2 from Parent.Child1

    }

    public class Parent

    {

        public int Id {get;set;}

        public Child1 Child1 {get;set;}

    }

    public class Child1

    {

        public int Id {get;set;}

    }

    public class Child2

    {

        public int Id {get;set;}

    }

}