Set serializer field as neither writeable or readable

[stephappiah]

Serializer fields like 'notify_email' are for operational purposes and not for representing or writing to the model object. The field only runs a function if set to true or pass if false.

[tomchristie]

I don't really see us adding much in the way of new functionality at this point.

You'd need to implement this as a custom field in your own codebase.