using System;

using System.Collections.Generic;

using AutoMapper;

using System.Linq;

using AutoMapper.EquivalencyExpression;

public class Program

{

    public class TopEntity

    {

        public Guid Id { get; set; }

​

        public ICollection<BottomEntity> Bottoms { get; set; }

    }

​

    public class BottomEntity

    {

        public Guid Id { get; set; }

        public DateTime Begin {get;set;}

​

        public Guid TopId { get; set; }

    }

​

    public class TopEntityViewModel

    {

        public Guid Id { get; set; }

​

        public ICollection<BottomEntityViewModel> Bottoms { get; set; }

    }

​

    public class BottomEntityViewModel

    {

        public Guid Id { get; set; }

        public DateTime Begin {get;set;}

    }

    public static void Main()

    {

            var mapperConfig = new MapperConfiguration(exp =>

            {

                exp.AddCollectionMappers();

                exp.CreateMap<TopEntity, TopEntityViewModel>();

​

                exp.CreateMap<BottomEntity, BottomEntityViewModel>();

​

                exp.CreateMap<TopEntityViewModel, TopEntity>();

​

                exp.CreateMap<BottomEntityViewModel, BottomEntity>()

                    .ForMember(dest => dest.TopId, opts => opts.Ignore())

                    .EqualityComparison((src, dest) => src.Begin == dest.Begin)

                    ;

            });

​

            mapperConfig.AssertConfigurationIsValid();

            var mapper = mapperConfig.CreateMapper();

​

            var topEntityId = Guid.NewGuid();

            var bottomEntityId1 = Guid.NewGuid();

            var bottomEntityId2 = Guid.NewGuid();

            var topEntity = new TopEntity

            {

                Id = topEntityId,

                Bottoms = new List<BottomEntity>

                {

                    new BottomEntity

                    {

                        Id = bottomEntityId1,

                        Begin = new DateTime(2023,8,8),

                        TopId = topEntityId

                    },

                    new BottomEntity

                    {

                        Id = bottomEntityId2,

                        Begin = new DateTime(2023,8,7),

                        TopId = topEntityId

                    }

                }

            };

​

            var topEntityVm = new TopEntityViewModel

            {

                Id = topEntityId,

                Bottoms = new List<BottomEntityViewModel>

                {

                    new BottomEntityViewModel

                    {

                        Id = bottomEntityId1,

                    },

                    new BottomEntityViewModel

                    {

                        Id = bottomEntityId2,

                        Begin = new DateTime(2023,8,8),

                    }

                }

            };

​

            var updatedTopEntity = mapper.Map(topEntityVm, topEntity);

​

            Console.WriteLine(updatedTopEntity.Bottoms.ElementAt(0).TopId);

            Console.WriteLine(updatedTopEntity.Bottoms.ElementAt(1).TopId);

            Console.WriteLine(updatedTopEntity.Bottoms.Count());

            Console.WriteLine(updatedTopEntity == topEntity);

    }

}