Ability to set MongoDB optional fields to `undefined`

Problem

Currently, optional fields in MongoDB have the type T | null, while sometimes we want to have really optional field, so it should be T | undefined. It would be nice to have some mechanism to distinguish between null and undefined

[dpetrick]

I personally thought about not actually storing undefined, but removing property when undefined is explicitly passed

undefined is also not really a value (with my non-JS perspective), it’s a property of the data (being absent), so storing it doesn’t make sense. We also talked to Mongo and they’re pushing hard for undefined not being a value / type, so that’s aligned with them.

So yea, anyway, we introduced unset for optional fields in 3.11.1, which achieves the main part of this request: The ability to remove values from documents.

The remaining issue is telling null and undefined apart somehow (e.g. when fetching fields that don’t exist on the document, we currently return null) and unfortunately this is much harder and likely requires a lot of API work. However, I do not consider this part of this issue, which is why I consider this issue closed.

To summarize: You can now unset composite and scalar fields in update operations. If you do not specify a field in a create operation, then it will not be null, but unset (undefined, missing, whatever you want to call it) on the document.

We will follow up soon with another ticket about better distinguishing null and undefined.

[dpetrick]

FYI follow-up for telling null and undefined apart: https://github.com/prisma/prisma/issues/12555