Serialize and Deserialize Derived Types with Json.net

Introduction

When working with Json.net, it is common to have a scenario where you need to serialize and deserialize derived types. This can be a bit tricky, but with the right approach, it can be done easily and efficiently.

Serializing Derived Types

To serialize derived types, you need to use the JsonConverter class. This class allows you to write a custom converter that will handle the serialization of your derived types.

First, you need to create a class that extends from JsonConverter. This class will contain the logic for serializing and deserializing your derived types. Here's an example:

public class AnimalConverter : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return objectType == typeof(Animal);
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        JObject jo = JObject.Load(reader);

        if (jo["type"].Value<string>() == "cat")
        {
            return jo.ToObject<Cat>();
        }
        else if (jo["type"].Value<string>() == "dog")
        {
            return jo.ToObject<Dog>();
        }
        else
        {
            throw new NotImplementedException();
        }
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        JObject jo = new JObject();
        jo.Add("type", value.GetType().Name);
        jo.Merge(JObject.FromObject(value));
        jo.WriteTo(writer);
    }
}

In this example, we're serializing two derived types: Cat and Dog. We're using a custom "type" property to differentiate between the two types.

To use this converter, you need to add it to your JsonSerializerSettings object. Here's an example:

var settings = new JsonSerializerSettings();
settings.Converters.Add(new AnimalConverter());

var json = JsonConvert.SerializeObject(animals, settings);

In this example, we're serializing a list of animals that contains both cats and dogs. We're using the custom AnimalConverter to serialize the derived types.

Deserializing Derived Types

To deserialize derived types, you need to use the same JsonConverter class. Here's an example:

var settings = new JsonSerializerSettings();
settings.Converters.Add(new AnimalConverter());

var animals = JsonConvert.DeserializeObject<List<Animal>>(json, settings);

In this example, we're deserializing a list of animals that contains both cats and dogs. We're using the same custom AnimalConverter to deserialize the derived types.

Conclusion

Serializing and deserializing derived types with Json.net can be a bit tricky, but with a custom JsonConverter, it can be done easily and efficiently. By following the steps outlined in this article, you can handle the serialization and deserialization of your derived types with ease.