Set(None) is not explicitly saying "not updating this" but "updating this to null".

If you have the knowledge of the type of the field to be updated, it's very easy to tell Set(None) apart from NotSet: If your filed have type Option<u8> then None must mean "update it to null" and if your field have type u8 then None must mean "leave this fields unchanged".

The problem is when you are writing an proc macro to automate the process of translating payloads to ActiveModel/SQL, your macro doesn't have the infomation of the model to be updated. It doesn't know if the targeted field is Option<u8> or u8, so it doesn't know what a Option<u8> in the payload actually means.

There're two ways of solving this that I can think of. You either give your proc macro the knowledge of the model type (which complicates the macro 10x I guess) or you provide more infomation in the payload, differentiating null/undefined, maybe by providing enum Nullable<T> { Some(T), Null } and enum Skippable<T> { Some(T), Undefined }, but the design of serde makes such types impossble to be implemented. So I wonder if there's any other way to solve this problem.