using System;

using System.Linq;

using System.Collections;

using System.Collections.Generic;

using Newtonsoft.Json;

using AutoMapper;

using AutoMapper.EquivalencyExpression;

public class Program

{

    public static void Main()

    {

        var config = new MapperConfiguration(cfg =>

        {

            cfg.AddCollectionMappers();

            cfg.CreateMap<SubItem, DestinationSubItem>().EqualityComparison((src, dest) => src.Id == dest.Id);

​

            cfg.CreateMap<SourceItem, DestinationItem>().EqualityComparison((src, dest) => src.Id == dest.Id);

                /*.ForMember(dest => dest.SubItems, opt => opt.MapFrom((src, dest, destMember, context) =>

                {

                    var mergedSubItems = dest.SubItems ?? new List<DestinationSubItem>();

                    foreach (var subItem in src.SubItems)

                    {

                        var existingSubItem = mergedSubItems.FirstOrDefault(d => d.Id == subItem.Id);

                        if (existingSubItem == null)

                        {

                            mergedSubItems.Add(context.Mapper.Map<DestinationSubItem>(subItem));

                        }

                        else

                        {

                            context.Mapper.Map(subItem, existingSubItem);

                        }

                    }

                    return mergedSubItems;

                }));

*/

            cfg.CreateMap<SourceClass, DestinationClass>();

            /*  .ForMember(dest => dest.Items, opt => opt.MapFrom((src, dest, destMember, context) =>

                {

                    var mergedItems = dest.Items ?? new List<DestinationItem>();

                    foreach (var item in src.Items)

                    {

                        var existingItem = mergedItems.FirstOrDefault(d => d.Id == item.Id);

                        if (existingItem == null)

                        {

                            mergedItems.Add(context.Mapper.Map<DestinationItem>(item));

                        }

                        else

                        {

                            context.Mapper.Map(item, existingItem);

                        }

                    }

                    return mergedItems;

                }));

                */

        });

​

        var mapper = config.CreateMapper();

        var source = new SourceClass

        {

            Items = new List<SourceItem>

            {

                new SourceItem

                {

                    Id = 1,

                    Name = "SourceItem1",

                    SubItems = new List<SubItem>

                    {

                        new SubItem { Id = 1, Description = "SourceSubItem1" }

                    }

                },

                new SourceItem

                {

                    Id = 2,

                    Name = "SourceItem2",

                    SubItems = new List<SubItem>

                    {

                        new SubItem { Id = 1, Description = "SourceSubItem2" }

                    }

                }

            }

        };

​

        var destination = new DestinationClass

        {

            Items = new List<DestinationItem>

            {

                new DestinationItem

                {

                    Id = 1,

                    Name = "DestinationItem1",

                    SubItems = new List<DestinationSubItem>

                    {

                        new DestinationSubItem { Id = 1, Description = "DestinationSubItem1" },

                        new DestinationSubItem { Id = 2, Description = "DestinationSubItem2" }

                    }

                },          

                new DestinationItem

                {

                    Id = 2,

                    Name = "DestinationItem2",

                    SubItems = new List<DestinationSubItem>

                    {

                        new DestinationSubItem { Id = 3, Description = "DestinationSubItem3" },

                        new DestinationSubItem { Id = 4, Description = "DestinationSubItem4" }

                    }

                }

            }

        };

​

        var finalDestination = mapper.Map(source, destination);

        Console.WriteLine(JsonConvert.SerializeObject(source));

        Console.WriteLine();

        Console.WriteLine(JsonConvert.SerializeObject(destination));

        Console.WriteLine();

        Console.WriteLine(JsonConvert.SerializeObject(finalDestination));

        Console.WriteLine("Hello World");

    }

}

​

public class SubItem

{

    public int Id { get; set; }

    public string Description { get; set; }

}

​

public class SourceItem

{

    public int Id { get; set; }

    public string Name { get; set; }

    public List<SubItem> SubItems { get; set; }

}

​

public class SourceClass

{

    public List<SourceItem> Items { get; set; }

}

​

public class DestinationSubItem

{

    public int Id { get; set; }

    public string Description { get; set; }

}

​

public class DestinationItem

{

    public int Id { get; set; }

    public string Name { get; set; }

    public List<DestinationSubItem> SubItems { get; set; }

}

​

public class DestinationClass

{

    public List<DestinationItem> Items { get; set; }

}