DbErr::RecordNotFound instead of DbErr::RecordNotUpdated when the record doesn't exist

[daalfox]

I think when you try to call update on an ActiveModel that does not exist, it should return a RecordNotFound instead of RecordNotUpdated.

This makes it possible to try to update without knowing the record exists, when update returns RecordNotUpdated you don't really know that the record is missing or there is some other issue with update. This is specially helpful on rest apis when you receive the response and you know that you should return a 500 error or a 404 with a single database query.

If you agree I can make a PR

[tyt2y3]

Changing error variant is a breaking change, but it's worth considering.

However I am not sure whether we can actually distinguish between RecordNotFound and RecordNotUpdated in general.

Can you do some investigation on MySQL and Postgres to demonstrate the logic?

[daalfox]

Now that I'm thinking about it, it's not that beneficial, You need to query the whole table to find out the item is missing anyways