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QueryPublisher unsubscribes after one event #86
Description
Is there an existing issue?
- I have searched existing issues
Build info
- ObjectBox version: 4.0.0
Steps to reproduce
let query: Query<Person> = ......
query.publisher
.replaceError(with: [])
/*.assign(to: \.persons, on: viewModel)*/
.sink(receiveValue: { persons in
viewModel.persons = persons
})
.store(in: &cancellables)Expected behavior
I expected that viewModel.persons will update continuously when I add / change a record that will match my query.
Actual behavior
After the initial query result is consumed by the Subscriber, QueryPublisher will unsubscribe because various Subscriber implementations like sink(), assign(to:) or onReceive() of a SwiftUI view will return Subscriber.Demand.none which causes QueryPublisher to signal completion to the Subscriber and shut down.
Activity
kemkriszt commentedon Sep 25, 2024
I'm also curious of how to handle this, I ended up creating a custom subscriber that after every
receiverequests unlimited but it seems like an ugly hack to megreenrobot-team commentedon Sep 30, 2024
Thanks for reporting. The current publisher implementation indeed does send the
finishedevent once it receives anonedemand (so demand for 0) from the subscriber.I guess the underlying issue is that it uses
Query.subscribe()behind the scenes which does not have a concept for demand. We should probably have a look at improving this, or maybe someone has an idea for an improvement?And so I think the current workaround is to use the subscribe APIs (like in the example) instead.
(There is also an internal issue to improve SwiftUI support at
objectbox/objectbox-swift#134.)