Primary keys should allow to be nullable

[nirinchev]

Right now we prevent primary keys from being nullable, but there's no reason for this. We should allow it.

[ianpward]

Or should we ?

[nirinchev]

We should 😄

[blagoev]

I would like to understand more. Even though core supports it why would we allowing this. I would argue this in 110% of the cases is a mistake when defining the schema. What's the use case we are trying to cover?

[dotjon0]

The @PrimaryKey() is the UID for the DB document (https://www.mongodb.com/docs/realm/sdk/flutter/realm-database/define-realm-object-schema/#primarykey) so can not be null - how would we uniquely identify each DB document otherwise? It would be good as @blagoev mentioned to hear the full use case.

[nirinchev]

null is a valid primary key/document id value in Realm/MongoDB. There can be exactly one object with primary key value equal to null the same way there can only be one object with a primary key value equal to 0 or "".

[dotjon0]

It would be good to understand the use case of having a null @PrimaryKey() DB document UID. Within our firm we always use unique ObjectID's for UIDs in order to keep our UIDs in a consistent format and data type - the same approach MongoDB Atlas functions as default if the _id UID is not provided when creating a document.

[nirinchev]

If you're using ObjectId/UUID for your primary key type, then null is unlikely to be useful value. But Realm also supports int and string primary keys and there null is just another value that may have meaning to some - e.g. if you are storing user settings in a table, null could indicate the default settings and personalized settings can be stored with the user id as the primary key value.

Ultimately, this issue is about consistency across our products. All other SDKs and MongoDB/Atlas Device Sync support nullable primary keys and so should we. If that's not something you need, you are by no means forced to use it - it's completely optional.