How to Fetch Records from CloudKit Not in My Local Cache - cloudkit

Question

I have an app that uses CloudKit for sync and I maintain a local cache of records. I have run into a sync scenario that I can't figure out.
I'm using the Public database and when my app is opened, I want to be able to go get all the updated records that my app missed while it was closed, or on a device where the app was just installed.
I can get the updated records by creating a NSPredicate to compare the modificationDate like this:
let predicate = NSPredicate(format: "modificationDate > %#", syncTimestamp as CVarArg)
let query = CKQuery(recordType: recordType, predicate: predicate)
But the part I can't figure out is how to get only the records that have been added to, or removed from, the CloudKit server.
Does anyone know how to do this? I know Apple provides a way for this in the Private database but I'm using the Public one here.
The only thing I can think of so far is to query all the reocrds of a certain recordType, collect all their recordNames and compare to my local cache. But it'd be nice to have smarter way than just pull large amounts of data and comparing huge arrays of recordNames.

Answer 1

CKQuerySubscription(recordType: myRecordType, predicate: predicate, options: [.firesOnRecordCreation, .firesOnRecordDeletion]) works perfectly on public DB.
Here's a code snippet (saving subscription is done with RxCloudKit, but this is beyond the point) -
let predicate = NSPredicate(format: "TRUEPREDICATE")
// the options are different from what you need, just showcasing the possibilities:
let subscription = CKQuerySubscription(recordType: recordTypeTest, predicate: predicate, options: [.firesOnRecordCreation, .firesOnRecordUpdate, .firesOnRecordDeletion, .firesOnce])
let info = CKNotificationInfo()
info.alertLocalizationKey = "NEW_PARTY_ALERT_KEY"
info.soundName = "NewAlert.aiff"
info.shouldBadge = true
subscription.notificationInfo = info
self.publicDB.rx.save(subscription: subscription).subscribe { event in
switch event {
case .success(let subscription):
print("subscription: ", subscription)
case .error(let error):
print("Error: ", error)
default:
break
}
}.disposed(by: self.disposeBag)