Json.NET different json structure, based on enum value

The reason you are getting the Self referencing loop detected exception is that the WriteJson method of your converter is calling itself recursively. When you apply a converter to a type using [JsonConverter(typeof(ConfigurationCustomConverter))], the WriteJson() method will unconditionally replace Json.NET's default implementation. Thus your inner call:

public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer) { //my changes here serializer.Serialize(writer, value); } 

would cause a stack overflow. Json.NET notices this and instead throws the exception you see. For more details, see JSON.Net throws StackOverflowException when using [JsonConvert()]. Setting ReferenceLoopHandling.Ignore simply causes the infinite recursion to be skipped, leaving your object empty.

You have a few options to solve this problem:

1. You could manually write all property names and values other than Type and TypeAdditionalData then write out the custom "type" property last. For instance:

   [JsonConverter(typeof(ConfigurationConverter))] public class Configuration { [JsonProperty(PropertyName = "name")] public string Name { get; set; } public MyEnumTypes Type { get; set; } public OptionalType TypeAdditionalData { get; set; } [JsonProperty(PropertyName = "value")] public int Value { get; set; } } class ConfigurationConverter : JsonConverter { const string typeName = "type"; public override bool CanConvert(Type objectType) { return typeof(Configuration).IsAssignableFrom(objectType); } public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer) { if (reader.TokenType == JsonToken.Null) return null; var config = (existingValue as Configuration ?? (Configuration)serializer.ContractResolver.ResolveContract(objectType).DefaultCreator()); // Populate the regular property values. var obj = JObject.Load(reader); var type = obj.RemoveProperty(typeName); using (var subReader = obj.CreateReader()) serializer.Populate(subReader, config); // Populate Type and OptionalType if (type is JValue) // Primitive value { config.Type = type.ToObject<MyEnumTypes>(serializer); } else { var dictionary = type.ToObject<Dictionary<MyEnumTypes, OptionalType>>(serializer); if (dictionary.Count > 0) { config.Type = dictionary.Keys.First(); config.TypeAdditionalData = dictionary.Values.First(); } } return config; } public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer) { var config = (Configuration)value; var contract = (JsonObjectContract)serializer.ContractResolver.ResolveContract(config.GetType()); writer.WriteStartObject(); foreach (var property in contract.Properties .Where(p => p.Writable && (p.ShouldSerialize == null || p.ShouldSerialize(config)) && !p.Ignored)) { if (property.UnderlyingName == "Type" || property.UnderlyingName == "TypeAdditionalData") continue; var propertyValue = property.ValueProvider.GetValue(config); if (propertyValue == null && serializer.NullValueHandling == NullValueHandling.Ignore) continue; writer.WritePropertyName(property.PropertyName); serializer.Serialize(writer, propertyValue); } writer.WritePropertyName(typeName); if (config.Type.GetCustomAttributeOfEnum<OptionalSettingsAttribute>() == null) { serializer.Serialize(writer, config.Type); } else { var dictionary = new Dictionary<MyEnumTypes, OptionalType> { { config.Type, config.TypeAdditionalData }, }; serializer.Serialize(writer, dictionary); } writer.WriteEndObject(); } } public class OptionalType { public string setting1 { get; set; } } public class OptionalSettingsAttribute : System.Attribute { public OptionalSettingsAttribute() { } } [JsonConverter(typeof(StringEnumConverter))] public enum MyEnumTypes { [EnumMember(Value = "simple1")] Simple1, [EnumMember(Value = "simple2")] Simple2, [OptionalSettingsAttribute] [EnumMember(Value = "optional1")] Optional1, [EnumMember(Value = "optional2")] [OptionalSettingsAttribute] Optional2 } public static class EnumExtensions { public static TAttribute GetCustomAttributeOfEnum<TAttribute>(this Enum value) where TAttribute : System.Attribute { var type = value.GetType(); var memInfo = type.GetMember(value.ToString()); return memInfo[0].GetCustomAttribute<TAttribute>(); } } public static class JsonExtensions { public static JToken RemoveProperty(this JObject obj, string name) { if (obj == null) return null; var property = obj.Property(name); if (property == null) return null; var value = property.Value; property.Remove(); property.Value = null; return value; } } 

   Notice I added [JsonConverter(typeof(StringEnumConverter))] to your enum. This ensures the type is always written as a string.

   Sample fiddle.

2. You could disable recursive calls to the converter via the technique shown in JSON.Net throws StackOverflowException when using [JsonConvert()], generate a default serialization, modify it as required, and write it out.

3. You could avoid the use of a converter entirely by marking Type and TypeAdditionalData as [JsonIgnore] and introducing an additional private property to serialize and deserialize "type":

   public class Configuration { [JsonProperty(PropertyName = "name")] public string Name { get; set; } [JsonIgnore] public MyEnumTypes Type { get; set; } [JsonIgnore] public OptionalType TypeAdditionalData { get; set; } [JsonProperty("type")] JToken SerializedType { get { if (Type.GetCustomAttributeOfEnum<OptionalSettingsAttribute>() == null) { return JToken.FromObject(Type); } else { var dictionary = new Dictionary<MyEnumTypes, OptionalType> { { Type, TypeAdditionalData }, }; return JToken.FromObject(dictionary); } } set { if (value == null || value.Type == JTokenType.Null) { TypeAdditionalData = null; Type = default(MyEnumTypes); } else if (value is JValue) { Type = value.ToObject<MyEnumTypes>(); } else { var dictionary = value.ToObject<Dictionary<MyEnumTypes, OptionalType>>(); if (dictionary.Count > 0) { Type = dictionary.Keys.First(); TypeAdditionalData = dictionary.Values.First(); } } } } [JsonProperty(PropertyName = "value")] public int Value { get; set; } }