How can I "un-JsonIgnore" an attribute in a derived class?

Question

I am using Newtonsoft's JsonSerializer to serialise some classes.

As I wanted to omit one field of my class in the serialisation process, I declared it as follow:

[JsonIgnore]
public int ParentId { get; set; }

This worked, but I am now facing a new problem : In a derived class, I would like this field to appear (and do so only in this specific derived class).

I have been looking through the documentation and on the Internet for a way to override this setting in child classes (I guess I need something like [JsonStopIgnore], but I couldn't find anything close).

---

• Is there any way for me to force JsonSerializer to pick up again this attribute ?
• Is it possible to explicitly mark an attribute as [JsonIgnore], but only in base class ?

Answer 1

The only way to "override" the behavior of the [JsonIgnore] attribute is to use a contract resolver, as @Yuval Itzchakov nicely explained in his answer.

However, there is another possible solution that might work for you: instead of using a [JsonIgnore] attribute, you could implement a ShouldSerializeParentId() method in your classes to control whether the ParentId property gets serialized. In the base class, make this method return false; then, override the method in the derived class to return true. (This feature is known as conditional property serialization in Json.Net.)

public class Base
{
    public int Id { get; set; }
    public int ParentId { get; set; }

    public virtual bool ShouldSerializeParentId()
    {
        return false;
    }
}

public class Derived : Base 
{ 
    public override bool ShouldSerializeParentId()
    {
        return true;
    }
}

Fiddle: https://dotnetfiddle.net/65sCSz