using System;

using System.Collections.Generic;

using System.Linq;

using Newtonsoft.Json;

using Newtonsoft.Json.Serialization;

public class Program

{

    public static void Main()

    {

        var results = new List<MyDto>

        {

            new MyDto 

            {

                Identifier = new KeyValuePair<string, string>("Car", "Ford"),

                Value1 = 13,

                Value2 = "A"

            },

            new MyDto 

            {

                Identifier = new KeyValuePair<string, string>("Train", "Bombardier"),

                Value1 = 14,

                Value2 = "B"

            },

        };

​

        var settings = new JsonSerializerSettings

        {

            Converters = new List<JsonConverter> { new MyDtoConverter() },

            Formatting = Formatting.Indented

        };

​

        string json = JsonConvert.SerializeObject(results, settings);

        Console.WriteLine(json);

    }

}

​

public class MyDto

{

    public KeyValuePair<string, string> Identifier { get; set; }

    public double Value1 { get; set; }

    public string Value2 { get; set; }

}

​

public class MyDtoConverter : JsonConverter

{

    public override bool CanConvert(Type objectType)

    {

        return objectType == typeof(MyDto);

    }

​

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)

    {

        MyDto dto = (MyDto)value;

        writer.WriteStartObject();

        writer.WritePropertyName(dto.Identifier.Key);

        writer.WriteValue(dto.Identifier.Value);

        var contract = (JsonObjectContract)serializer.ContractResolver.ResolveContract(typeof(MyDto));

        foreach (JsonProperty prop in contract.Properties.Where(p => p.PropertyName != nameof(MyDto.Identifier)))

        {

            writer.WritePropertyName(prop.PropertyName);

            writer.WriteValue(prop.ValueProvider.GetValue(dto));

        }

        writer.WriteEndObject();

    }

​

    public override bool CanRead => false;

​

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)

    {

        throw new NotImplementedException();

    }

}

​