using System;

using System.Collections.Generic;

using Newtonsoft.Json;

public class Program

{

    public static void Main()

    {

        var jsonToOne = "{'data': { 'type': 'Test', 'id': '1' } }";

        var jsonToMany = "{'data': [{ 'type': 'Test', 'id': '1' }, { 'type': 'Test', 'id': '2' }]}";

        var resultToOne = JsonConvert.DeserializeObject<Relation>(jsonToOne);

        var resultToMany = JsonConvert.DeserializeObject<Relation>(jsonToMany);

        Console.WriteLine("Type of to one: " + resultToOne.GetType());

        Console.WriteLine("Type of to many: " + resultToMany.GetType());

    }

    [JsonConverter(typeof(RelationshipConverter))]

    private abstract class Relation

    {

        [JsonProperty("meta")]

        public Dictionary<string, object> Meta { get; set; }

    }

    private class ToOneRelation : Relation

    {

        [JsonProperty("data")]

        public object Data { get; set; }

    }

    private class ToManyRelation : Relation

    {

        [JsonProperty("data")]

        public List<object> Data { get; set; }

    }

    private class RelationshipConverter : JsonConverter

    {

        public override bool CanWrite { get { return false; } }

        public override bool CanConvert(Type objectType)

        {

            return objectType == typeof(Relation);

        }

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

        {

            throw new NotSupportedException();

        }

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

        {

            if (reader.TokenType == JsonToken.StartObject)

            {

                object toOneData = null;

                List<object> toManyRelationshipData = null;

                Dictionary<string, object> meta = null;

​

                reader.Read();

                while (reader.TokenType == JsonToken.PropertyName)

                {

                    string propertyName = reader.Value.ToString();

                    reader.Read();

                    if (string.Equals(propertyName, "data", StringComparison.OrdinalIgnoreCase))

                    {

                        if (reader.TokenType == JsonToken.StartObject)

                        {

                            toOneData = serializer.Deserialize<object>(reader);

                        }

                        else if (reader.TokenType == JsonToken.StartArray)

                        {

                            toManyRelationshipData = serializer.Deserialize<List<object>>(reader);

                        }

                    }

                    else if (string.Equals(propertyName, "meta", StringComparison.OrdinalIgnoreCase))

                    {

                        meta = serializer.Deserialize<Dictionary<string, object>>(reader);

                    }

                    else

                    {

                        reader.Skip();

                    }

                    reader.Read();

                }

​

                if (toManyRelationshipData == null)

                {

                    return new ToOneRelation

                    {

                        Data = toOneData,

                        Meta = meta

                    };

                }

                else

                {

                    return new ToManyRelation

                    {

                        Data = toManyRelationshipData,

                        Meta = meta

                    };

                }

            }

​

            return null;

        }

    }

}