How to implement custom JsonConverter in JSON.NET?

Using the standard CustomCreationConverter, I was struggling to work how to generate the correct type (Person or Employee), because in order to determine this you need to analyse the JSON and there is no built in way to do this using the Create method.

I found a discussion thread pertaining to type conversion and it turned out to provide the answer. Here is a link: Type converting (archived link).

What’s required is to subclass JsonConverter, overriding the ReadJson method and creating a new abstract Create method which accepts a JObject.

The JObject class provides a means to load a JSON object and
provides access to the data within this object.

The overridden ReadJson method creates a JObject and invokes the Create method (implemented by our derived converter class), passing in the JObject instance.

This JObject instance can then be analysed to determine the correct type by checking existence of certain fields.


string json = "[{
        \"Department\": \"Department1\",
        \"JobTitle\": \"JobTitle1\",
        \"FirstName\": \"FirstName1\",
        \"LastName\": \"LastName1\"
        \"Department\": \"Department2\",
        \"JobTitle\": \"JobTitle2\",
        \"FirstName\": \"FirstName2\",
        \"LastName\": \"LastName2\"
        {\"Skill\": \"Painter\",
        \"FirstName\": \"FirstName3\",
        \"LastName\": \"LastName3\"

List<Person> persons = 
    JsonConvert.DeserializeObject<List<Person>>(json, new PersonConverter());


public class PersonConverter : JsonCreationConverter<Person>
    protected override Person Create(Type objectType, JObject jObject)
        if (FieldExists("Skill", jObject))
            return new Artist();
        else if (FieldExists("Department", jObject))
            return new Employee();
            return new Person();

    private bool FieldExists(string fieldName, JObject jObject)
        return jObject[fieldName] != null;

public abstract class JsonCreationConverter<T> : JsonConverter
    /// <summary>
    /// Create an instance of objectType, based properties in the JSON object
    /// </summary>
    /// <param name="objectType">type of object expected</param>
    /// <param name="jObject">
    /// contents of JSON object that will be deserialized
    /// </param>
    /// <returns></returns>
    protected abstract T Create(Type objectType, JObject jObject);

    public override bool CanConvert(Type objectType)
        return typeof(T).IsAssignableFrom(objectType);

    public override bool CanWrite
        get { return false; }

    public override object ReadJson(JsonReader reader, 
                                    Type objectType, 
                                     object existingValue, 
                                     JsonSerializer serializer)
        // Load JObject from stream
        JObject jObject = JObject.Load(reader);

        // Create target object based on JObject
        T target = Create(objectType, jObject);

        // Populate the object properties
        serializer.Populate(jObject.CreateReader(), target);

        return target;

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