Observe C(R)UD events

[MartinP7r]

Hello 👋🏼

With ValueObservation we can track changes to the database based on a tracked value.

Tracked changes are insertions, updates, and deletions

Is there a way to observe insert/delete/update of rows directly and get back the objects that were inserted/deleted, e.g. as a PassthroughSubject?

I'm imagining an API along the lines of

ValueObservation(events: [.deletion])
  .tracking(Player.self)
  .publisher(in: db.reader)

If it's already available and I overlooked it in the docs I'm very sorry!

[groue]

Hello @MartinP7r,

You can turn a ValueObservation into a Combine publisher, with the same api as the one you are imagining.

For details, see GRDB ❤️ Combine.

For more usages of ValueObservation (including Combine, but also asynchronous sequences), see ValueObservation Usage.

[groue]

Oops, my initial answer is off topic.

Is there a way to observe insert/delete/update of rows directly and get back the objects that were inserted/deleted.

You can build this from the low-level TransactionObserver protocol. You'll get there the most information that SQLite can provide about database changes.

[groue]

You have other options to evaluate:

• deleteAndFetchAll (new in GRDB 6) which deletes, and returns the deleted rows.
• A trigger that populates a table of deleted rows, which you can observe.

[MartinP7r]

You're right, this doesn't help me as I'm trying to observe deleted items from a separate part of the app before discarding them.
Conceptually trigger or a pre-update hook seem to be my best options here.
I any case, thank you for showing me all these different paths of possible solutions! 🤗

[groue]

All right :) I'm curious about the solution that will work for you!

[funct7]

I'm assuming that the OP wanted to receive only the "delta" not the end result. I think it might be a good extension to provide for people migrating from Realm.

[groue]

All contributions are welcome, @funct7. You might be interested in #1523 as well.