Comment by hx8

There's plenty of reasons to set a unique identifier before database save, or to want a unique identifier that doesn't have a 1-to-1 relationship with your object.

For example, in the idempotent kafka consumer pattern we set a unique ID in the header of every kafka message at the time of message publishing. We then have our consumers do a quick check of the ID against their data store to see if they have processed the message before or not. This way there is no impact if a consumer sees the same message twice. This allows us more flexibility during rebalancing events or replaying old offsets.