Copy nested Model object to DTO object using c#

I want to copy data object to data transfer object which is nested with the same type.

C#

public class Data
{
    public int Id { get; set; }
    public string SomeInfo { get; set; }
    public virtual ICollection<Data> Data { get; set; }
}

public class DTOData
{
    public int Id { get; set; }
    public string SomeInfo { get; set; }
    public virtual ICollection<DTOData> Data { get; set; }
}

List<Data> data = new List<Data>();
data.Add(new Data(){Id =1, SomeInfo  = 'sometext' });

List<DTOData> dtoData = new List<DTOData>();
dtoData.Add(new DTOData(){Id =10, SomeInfo  = 'sometext2' });

I want to copy data object to DTOData (data transfer object).

My approach

dtoData = (DTOData) data;

But it is throwing exception of type mismatch. How can I achive copying the data object to DTOData object, the main complexity with this is that it has nested self referencing. Please help.

Answers:

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Method 1

if you don’t care about performance this could be a solution, serialize and deserialize it to the new type using json and newtonsoft, something like:

dtoData  = JsonConvert.DeserializeObject<DTOData>(JsonConvert.SerializeObject(data));

in the case of a list object:

dtoData  = JsonConvert.DeserializeObject<List<DTOData>>(JsonConvert.SerializeObject(data));

Method 2

You need to explicitly transform each Data object into a new DTOData object one way or another.

You could for example do this iteratively using a Stack<T>. Something like this:

static List<DTOData> Map(List<Data> data)
{
    if (data == null)
        return null;

    var dtos = new List<DTOData>(data.Count);
    var stack = new Stack<(Data source, DTOData parent)>();
    foreach (var root in data)
    {
        //store the root nodes in the list to be returned
        var dto = new DTOData() { Id = root.Id, SomeInfo = root.SomeInfo };
        dtos.Add(dto);

        if (root.Data != null)
        {
            dto.Data = new List<DTOData>(root.Data.Count);
            foreach (var child in root.Data)
                stack.Push((child, dto));
        }

        //handle the child nodes
        while (stack.Count > 0)
        {
            var x = stack.Pop();
            dto = new DTOData() { Id = x.source.Id, SomeInfo = x.source.SomeInfo };

            if (x.parent != null)
                x.parent.Data.Add(dto);

            if (x.source.Data != null)
            {
                dto.Data = new List<DTOData>(x.source.Data.Count);
                foreach (var child in x.source.Data)
                    stack.Push((child, dto));
            }
        }
    }
    return dtos;
}

Method 3

You can use LINQ and query the original list to the new list.

List<DTOData> dtoData = data
    .Select(x => new DTOData(){Id =x.Id, SomeInfo  = x.SomeInfo })
    .ToList();

Here’s a console app that shows better.

using SelectMany;
using System;
using System.Collections.Generic;
using System.Linq;

var listOfAs = new List<A>
{
    new (new B[] { new (1, 2), new (3, 4) }),
    new (new B[] { new (5, 6), new (7, 8) })
};

var listOfDtos = listOfAs
    .SelectMany(a => a.Bs)
    .Select(b => new Dto(b.BCount1 + b.BCount2))
    .ToList();

foreach (var dto in listOfDtos) Console.WriteLine(dto.TotalCount);

namespace SelectMany
{
    public record A(IEnumerable<B> Bs);
    public record B(int BCount1, int BCount2);
    public record Dto(int TotalCount);
}

//output:
//3
//7
//11
//15

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0