How to automatically include type information when serializing?

Question

Is it possible to specify that I always want type-information in the json object when serializing a property in an class? (Ideally with Newtonsoft). I'm thinking something like this:

public abstract class Value {...}
public class BigValue : Value {...}
public class SmallValue : Value {...}

public class ValueContainer
{
    [JsonSetting(TypenameHandling = TypenameHandling.All)] // <--- Something like this?
    public Value TheValue { get; set; }
}

I am aware that I could specify this behavior when doing the parsing with a custom converter. But I want to include the typeinformation every time objects of this type is serialized, without manually having to specify which serialization options to use.

Yes it is, use a [custom converter](https://www.newtonsoft.com/json/help/html/CustomJsonConverter.htm) — Liam, Sep 03 '21 at 10:41
Yes, that is a solution, but then i would again have to manually specify that I want to use this converter each time that I have to serialize a `ValueContainer` object. Is there a way to specify it ones, and then not have to deal it again? — SørenHN, Sep 03 '21 at 10:50
@SørenHN it is the same as specifying `TypeNameHandling` - use `JsonPropertyAttribute`. — Guru Stron, Sep 03 '21 at 10:54
That very much depends on how your using Json.Net. You can often specify a default converter in things like web api. But you don't actually specify how your using Json.Net so I can't answer that question — Liam, Sep 03 '21 at 10:56
Seems [you can't override it "globally"](https://stackoverflow.com/questions/5881028/can-you-extend-the-default-jsonconverter-used-in-json-net-for-collections) — Liam, Sep 03 '21 at 10:58
Does this answer your question? [How to implement custom JsonConverter in JSON.NET?](https://stackoverflow.com/questions/8030538/how-to-implement-custom-jsonconverter-in-json-net) — Liam, Sep 03 '21 at 11:01

score 1 · Accepted Answer · answered Sep 03 '21 at 10:50

Newtonsoft.Json's JsonPropertyAttribute has TypeNameHandling property which you can set:

public class Root
{
    [JsonProperty(TypeNameHandling = TypeNameHandling.All)]
    public Base Prop { get; set; }
}
public class Base
{
    public int IntProp { get; set; }
}
public class Child:Base
{
}

// Example:
var result = JsonConvert.SerializeObject(new Root
{
    Prop = new Child()
});
Console.WriteLine(result);  // prints {"Prop":{"$type":"SOAnswers.TestTypeNamehandling+Child, SOAnswers","IntProp":0}}

How to automatically include type information when serializing?

1 Answers1