CustomDiscriminatorObjectConverter

CustomDiscriminatorObjectConverter.cs

using System;
using System.Diagnostics.Contracts;
using System.Linq;
using Newtonsoft.Json;
using Newtonsoft.Json.Linq;

namespace Hediet.Json.Converter
{
    public class CustomDiscriminatorObjectConverter : Newtonsoft.Json.JsonConverter
    {
        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)
        {
            var discrimatorKey = GetDiscriminatorKey(objectType);

            var obj = JObject.Load(reader);
            var discriminator = obj[discrimatorKey].Value<string>();
            obj.Remove(discrimatorKey);

            var type = ResolveDiscriminator(objectType, discriminator);

            return serializer.Deserialize(obj.CreateReader(), type);
        }

        protected virtual Type ResolveDiscriminator(Type type, string discriminator)
        {
            var attrs = type.GetCustomAttributes(typeof(DiscriminatedSubtypeAttribute), false).OfType<DiscriminatedSubtypeAttribute>();
            var attr = attrs.FirstOrDefault(a => a.Discriminator == discriminator);
            if (attr == null)
                return null;
            return attr.Type;
        }

        protected virtual string GetDiscriminatorKey(Type type)
        {
            var attr = type.GetCustomAttributes(typeof (DiscriminatedClassAttribute), false).OfType<DiscriminatedClassAttribute>().FirstOrDefault();
            if (attr == null)
                return null;
            return attr.DiscriminatorKey;
        }

        public override bool CanConvert(Type objectType)
        {
            if (!objectType.IsClass && !objectType.IsInterface)
                return false;

            var d = GetDiscriminatorKey(objectType);
            return d != null;
        }
    }
}

DiscriminatedClassAttribute.cs

using System;

namespace Hediet.Json.Converter
{
    [AttributeUsage(AttributeTargets.Class, Inherited = false, AllowMultiple = true)]
    public sealed class DiscriminatedClassAttribute : Attribute
    {
        public string DiscriminatorKey { get; private set; }

        public DiscriminatedClassAttribute(string discriminatorKey)
        {
            DiscriminatorKey = discriminatorKey;
        }
    }
}

DiscriminatedSubtypeAttribute.cs

using System;

namespace Hediet.Json.Converter
{
    [AttributeUsage(AttributeTargets.Class, Inherited = false, AllowMultiple = true)]
    public sealed class DiscriminatedSubtypeAttribute : Attribute
    {
        public string Discriminator { get; private set; }
        public Type Type { get; private set; }

        public DiscriminatedSubtypeAttribute(string discriminator, Type type)
        {
            Discriminator = discriminator;
            Type = type;
        }
    }
}