JSON.NET–Using a Custom Contract Resolver without loosing CamelCasing

For a project I’m working we created a custom ContractResolver to apply some localization magic before JSON data is send to the client.

Here is the code we are using:

	public class LocalizedContractResolver : CamelCasePropertyNamesContractResolver
	{
	protected override JsonContract CreateContract(Type objectType)
	{
	JsonContract contract = base.CreateContract(objectType);
	LocalizeAttribute localizeAttribute =
	(LocalizeAttribute)Attribute.GetCustomAttribute(objectType, typeof(LocalizeAttribute));
	if (localizeAttribute == null)
	return contract;
	contract.Converter = new LocalizedConverter(localizeAttribute.KeyField, localizeAttribute.LabelField);
	return contract;
	}
	}

view raw LocalizedContractResolver.cs hosted with ❤ by GitHub

	public class LocalizedConverter : JsonConverter
	{
	private string _keyField;
	private string _valueField;
	public LocalizedConverter(string keyField, string valueField)
	{
	_keyField = keyField;
	_valueField = valueField;
	}
	public override bool CanRead => false;
	public override bool CanConvert(Type objectType)
	{
	return true;
	}
	public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
	{
	//Should not be called because CanRead=false
	throw new NotImplementedException();
	}
	public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
	{
	JToken t = JToken.FromObject(value);
	if (t is JObject o)
	{
	o.Property(field).Value = "localized"; //Removed localization logic to simplify sample
	o.WriteTo(writer);
	}
	else
	{
	t.WriteTo(writer);
	}
	}
	}

view raw LocalizedConverter.cs hosted with ❤ by GitHub

	[Localize(KeyField =nameof(FirstName), LabelField =nameof(LastName))]
	public class User
	{
	public string FirstName { get; set; }
	public string LastName { get; set; }
	public int SnakeRating { get; set; }
	}
	}

view raw User.cs hosted with ❤ by GitHub

Let’s try this code:

	static void Main(string[] args)
	{
	User user = new User
	{
	FirstName = "Tom",
	LastName = "Riddle",
	SnakeRating = 10
	};
	string json = JsonConvert.SerializeObject(user, Formatting.Indented, new JsonSerializerSettings { ContractResolver = new LocalizedContractResolver() });
	Console.WriteLine(json);
	Console.ReadLine();
	}

view raw Program.cs hosted with ❤ by GitHub

As you can see the ContractResolver does its job, only problem is that we loose the CamelCasing. Here is how you can fix it:

	public class LocalizedConverter : JsonConverter
	{
	private string _keyField;
	private string _valueField;
	private CamelCasePropertyNamesContractResolver _resolver;
	public LocalizedConverter(string keyField, string valueField)
	{
	_keyField = keyField;
	_valueField = valueField;
	_resolver = new CamelCasePropertyNamesContractResolver(); ;
	}
	public override bool CanRead => false;
	public override bool CanConvert(Type objectType)
	{
	return true;
	}
	public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
	{
	//Should not be called because CanRead=false
	throw new NotImplementedException();
	}
	public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
	{
	JToken t = JToken.FromObject(value, new JsonSerializer() {
	ContractResolver = _resolver
	});
	if (t is JObject o)
	{
	var field = _resolver.GetResolvedPropertyName(_valueField);
	o.Property(field).Value = "localized";
	o.WriteTo(writer);
	}
	else
	{
	t.WriteTo(writer);
	}
	}
	}

view raw LocalizedConverter.cs hosted with ❤ by GitHub

Let’s run our code again: