Gorm doesnt allow updates of ids whose relations have been preloaded

[Fuzzyma]

GORM Playground Link

go-gorm/playground#834

Description

I spend multiple hours trying to figure out why a simple Save() wasnt working after I set some relation Ids to new values.

Turns out, when you preloaded the relation of that id field before, gorm does not allow to update the id.
It will reflect it in the struct, but will reset it back after while Save(). When using nullable fields with pointers, this also means, that the pointer is changed back to the old value which can lead to sideeffects when the pointer is used somewhere else.

In my case a simple settings.StateID = &state.ID lead to absolutely unexpected behavior.

I understand, that gorm does not want to get the preloaded model and the id out of sync but silently reverting it on save is even worse.

I would have expected an error that tells me the missmatch or just save the id without updating relations.