using System;

using System.Collections.Generic;

using System.Linq;

using Newtonsoft.Json;

​

​

public class RootOne

{

    public int Price { get; set; }

    public string Reference { get; set; }

    public int Idn { get; set; }

}

​

public class RootTwo {

    [JsonProperty("id_image")]

    public int ImageId { get; set; }

    public string Legend { get; set; }

}

​

public class Program

{

    public static void Main()

    {

        string jsonStrOne = "{\"1228\":{\"price\":836,\"reference\":\"243107210-01\",\"idn\":1228},\"1294\":{\"price\":864,\"reference\":\"243607210-01\",\"idn\":1294}}";

        string jsonStrTwo = "{\"1228\":[{\"id_image\":\"35298\",\"legend\":\"\"},{\"id_image\":\"35299\",\"legend\":\"\"},{\"id_image\":\"35300\",\"legend\":\"\"}],\"1294\":[{\"id_image\":\"35298\",\"legend\":\"\"},{\"id_image\":\"35299\",\"legend\":\"\"},{\"id_image\":\"35300\",\"legend\":\"\"}]}";

​

        var jsonOne = JsonConvert.DeserializeObject<Dictionary<int, RootOne>>(jsonStrOne);

        var jsonTwo = JsonConvert.DeserializeObject<Dictionary<int, List<RootTwo>>>(jsonStrTwo);

        var query = from listOne in jsonOne

                    from listTwo in jsonTwo

                    where listOne.Key == listTwo.Key

                    select new {Id = listOne.Key, Ref = listOne.Value.Reference, Images = listTwo.Value};

        foreach (var item in query)

        {

            Console.WriteLine("Id:" +item.Id);

            Console.WriteLine("Ref" +item.Ref);

            Console.WriteLine("Images:" + string.Join(",", item.Images.Select(x=>x.ImageId).ToArray()));

            Console.WriteLine("----------------------------------");

        }

    }

}