using System;

using System.Collections.Generic;

using System.Linq;

using Newtonsoft.Json;

using AutoMapper;

​

public class Program

{

    public static void Main()

    {

        var config = new MapperConfiguration(cfg =>

        {

            cfg.CreateMap<Assignment, AssignmentModel>();

            cfg.CreateMap<Response, ICollection<AssignmentModel>>()

                .ConvertUsing<ResponseAssignmentModelCollectionConverter>();

        });

        IMapper mapper = config.CreateMapper();

        var response = new Response{

            Assignments = new List<Assignment>

            {

                new Assignment{AssignmentId = 1, ProductId = 101}, 

                new Assignment{AssignmentId = 2, ProductId = 101}, 

            }, 

            Products = new List<Product>

            {

                new Product{ProductId = 101}, 

                new Product{ProductId = 102}

            }

        };

        var result = mapper.Map<ICollection<AssignmentModel>>(response);

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

    }

}

​

public class Response

{

    public List<Assignment> Assignments { get; set; }

​

    public List<Product> Products { get; set; }

}

​

public class Assignment

{

    public int AssignmentId { get; set; }

​

    public int ProductId { get; set; } // references Product.ProductId

}

​

public class Product

{

    public int ProductId { get; set; }

}

​

public class AssignmentModel

{

    public int AssignmentId { get; set; }

​

    public int ProductId { get; set; }

​

    public Product Product { get; set; }

}

​

public class ResponseAssignmentModelCollectionConverter : ITypeConverter<Response, ICollection<AssignmentModel>>

{

    public ICollection<AssignmentModel> Convert(Response source, ICollection<AssignmentModel> destination, ResolutionContext context)

    {

        var _mapper = context.Mapper;

        var result = _mapper.Map<List<AssignmentModel>>(source.Assignments);

        result = result.Join(source.Products, a => a.ProductId, b => b.ProductId, (a, b) =>

        {

            a.Product = b;

            return a;

        }).ToList();

        return result;

    }

}