Starting 20th March 2025, I see an increase in bandwidth and latency for one of my CloudKit projects. I'm using NSPersistentCloudKitContainer to synchronise my data. I haven't changed any CloudKit scheme during that time but shipped an update. Since then, I reverted some changes from that update, which could have led to changes in the sync behaviour. Is anyone else seeing any issues? I would love to file a DTS and use one of my credits for that, but unfortunately, I can't because I cannot reproduce it with a demo project because I cannot travel back in time and check if it also has an increase in metrics during that time. Maybe an Apple engineer can green-light me filing a DTS request, please.

Hello Apple Team, We are looking at developing an iOS feature on our current development that stores user-generated images as CKAssets in the public CloudKit database, with access control enforced by our app’s own logic (not CloudKit Sharing as that has a limit of 100 shares per device). Each story or post is a public record, and users only see content based on buddy relationships handled within the app. We’d like to confirm that this pattern is consistent with Apple’s best practices for social features. Specifically: Is it acceptable to store user-uploaded CKAssets in the public CloudKit database, as long as access visibility is enforced by the app? Are there any performance or quota limitations (e.g., storage, bandwidth, or user sync limits) that apply to CKAssets in the public database when used at scale? Would CloudKit Sharing be recommended instead, even if we don’t require user-to-user sharing invitations? For App Review, is this model (public CKAssets + app-enforced access control) compliant with Apple’s data and security expectations? Are there any caching or bandwidth optimization guidelines for handling image-heavy public CKAsset data in CloudKit? Thanks again for your time

I'm testing my app before releasing to testers, and my app (both macOS and iOS) is crashing when I perform one operation, but only in the production build. I have data that loads from a remote source, and can be periodically updated. There is an option to delete all of that data from the iCloud data store, unless the user has modified a record. Each table has a flag to indicate that (userEdited). Here's the function that is crashing: func deleteCommonData<T:PersistentModel & SDBuddyModel>(_ type: T.Type) throws { try modelContext.delete(model: T.self, where: #Predicate<T> { !$0.userEdited }) } Here's one of the calls that results in a crash: try modelManager.deleteCommonData(Link.self) Here's the error from iOS Console: SwiftData/DataUtilities.swift:85: Fatal error: Couldn't find \Link.<computed 0x0000000104b9d208 (Bool)> on Link with fields [SwiftData.Schema.PropertyMetadata(name: "id", keypath: \Link.<computed 0x0000000104b09b44 (String)>, defaultValue: Optional("54EC6602-CA7C-4EC7-AC06-16E7F2E22DE7"), metadata: nil), SwiftData.Schema.PropertyMetadata(name: "name", keypath: \Link.<computed 0x0000000104b09b84 (String)>, defaultValue: Optional(""), metadata: nil), SwiftData.Schema.PropertyMetadata(name: "url", keypath: \Link.<computed 0x0000000104b09bc4 (String)>, defaultValue: Optional(""), metadata: nil), SwiftData.Schema.PropertyMetadata(name: "desc", keypath: \Link.<computed 0x0000000104b09c04 (String)>, defaultValue: Optional(""), metadata: nil), SwiftData.Schema.PropertyMetadata(name: "userEdited", keypath: \Link.<computed 0x0000000104b09664 (Bool)>, defaultValue: Optional(false), metadata: nil), SwiftData.Schema.PropertyMetadata(name: "modified", keypath: \Link.<computed 0x0000000104b09c44 (Date)>, defaultVal<…> Here's a fragment of the crash log: Exception Type: EXC_BREAKPOINT (SIGTRAP) Exception Codes: 0x0000000000000001, 0x000000019373222c Termination Reason: Namespace SIGNAL, Code 5, Trace/BPT trap: 5 Terminating Process: exc handler [80543] Thread 0 Crashed: 0 libswiftCore.dylib 0x19373222c _assertionFailure(_:_:file:line:flags:) + 176 1 SwiftData 0x22a222160 0x22a1ad000 + 479584 2 SwiftData 0x22a2709c0 0x22a1ad000 + 801216 3 SwiftData 0x22a221b08 0x22a1ad000 + 477960 4 SwiftData 0x22a27b0ec 0x22a1ad000 + 844012 5 SwiftData 0x22a27b084 0x22a1ad000 + 843908 6 SwiftData 0x22a28182c 0x22a1ad000 + 870444 7 SwiftData 0x22a2809e8 0x22a1ad000 + 866792 8 SwiftData 0x22a285204 0x22a1ad000 + 885252 9 SwiftData 0x22a281c7c 0x22a1ad000 + 871548 10 SwiftData 0x22a27cf6c 0x22a1ad000 + 851820 11 SwiftData 0x22a27cc48 0x22a1ad000 + 851016 12 SwiftData 0x22a27a6b0 0x22a1ad000 + 841392 13 SwiftData 0x22a285b2c 0x22a1ad000 + 887596 14 SwiftData 0x22a285a10 0x22a1ad000 + 887312 15 SwiftData 0x22a285bcc 0x22a1ad000 + 887756 16 SwiftData 0x22a27cf6c 0x22a1ad000 + 851820 17 SwiftData 0x22a27cc48 0x22a1ad000 + 851016 18 SwiftData 0x22a27a6b0 0x22a1ad000 + 841392 19 SwiftData 0x22a27c0d8 0x22a1ad000 + 848088 20 SwiftData 0x22a27a654 0x22a1ad000 + 841300 21 SwiftData 0x22a1be548 0x22a1ad000 + 70984 22 SwiftData 0x22a1cfd64 0x22a1ad000 + 142692 23 SwiftData 0x22a1b9618 0x22a1ad000 + 50712 24 SwiftData 0x22a1d2e8c 0x22a1ad000 + 155276 25 CoreData 0x187fbb568 thunk for @callee_guaranteed () -> (@out A, @error @owned Error) + 28 26 CoreData 0x187fc2300 partial apply for thunk for @callee_guaranteed () -> (@out A, @error @owned Error) + 24 27 CoreData 0x187fc19c4 closure #1 in closure #1 in NSManagedObjectContext._rethrowsHelper_performAndWait<A>(fn:execute:rescue:) + 192 28 CoreData 0x187fbbda8 thunk for @callee_guaranteed @Sendable () -> () + 28 29 CoreData 0x187fbbdd0 thunk for @escaping @callee_guaranteed @Sendable () -> () + 28 30 CoreData 0x187f663fc developerSubmittedBlockToNSManagedObjectContextPerform + 252 31 libdispatch.dylib 0x180336ac4 _dispatch_client_callout + 16 32 libdispatch.dylib 0x18032c940 _dispatch_lane_barrier_sync_invoke_and_complete + 56 33 CoreData 0x187fd7290 -[NSManagedObjectContext performBlockAndWait:] + 364 34 CoreData 0x187fc1fb8 NSManagedObjectContext.performAndWait<A>(_:) + 544 35 SwiftData 0x22a1b877c 0x22a1ad000 + 46972 36 SwiftData 0x22a1be2a8 0x22a1ad000 + 70312 37 SwiftData 0x22a1c0e34 0x22a1ad000 + 81460 38 SwiftData 0x22a23ea94 0x22a1ad000 + 596628 39 SwiftData 0x22a256828 0x22a1ad000 + 694312 40 Sourdough Buddy 0x104e5dc98 specialized ModelManager.deleteCommonData<A>(_:) + 144 (ModelManager.swift:128) [inlined] 41 Sourdough Buddy 0x104e5dc98 closure #1 in SettingsView.clearStarterData.getter + 876 (SettingsView.swift:243) It works if I do the following instead: try modelContext.delete(model: Link.self, where: #Predicate { !$0.userEdited }) Why would the func call work in development, but crash in production? And why does doing the more verbose way work instead? I think this is a bug. Thanks

Hi everyone, In the simple app below, I have a QueryView that has LazyVStack containing 100k TextField's that edit the item's content. The items are fetched with a @Query. On launch, the app will generate 100k items. Once created, when I press any of the TextField's , a severe hang happens, and every time I type a single character, it will cause another hang over and over again. I looked at it in Instruments and it shows that the main thread is busy during the duration of the hang (2.31 seconds) updating QueryView. From the cause and effect graph, the update is caused by @Observable QueryController <Item>.(Bool). Why does it take too long to recalculate the view, given that it's in a LazyVStack? (In other words, why is the hang duration directly proportional to the number of items?) How to fix the performance of this app? I thought adding LazyVStack was all I need to handle the large dataset, but maybe I need to add a custom pagination with .fetchLimit on top of that? (I understand that ModelActor would be an alternative to @Query because it will make the database operations happen outside of the main thread which will fix this problem, but with that I will lose the automatic fetching of @Query.) Thank you for the help! import SwiftData import SwiftUI @main struct QueryPerformanceApp: App { var body: some Scene { WindowGroup { ContentView() .modelContainer(for: [Item.self], inMemory: true) } } } @Model final class Item { var name: String init(name: String) { self.name = name } } struct ItemDetail: View { @Bindable var item: Item var body: some View { TextField("Name", text: $item.name) } } struct QueryView: View { @Query private var items: [Item] var body: some View { ScrollView { LazyVStack { ForEach(items) { item in VStack { ItemDetail(item: item) } } } } } } struct ContentView: View { let itemCount = 100_000 @Environment(\.modelContext) private var context @State private var isLoading = true var body: some View { Group { if isLoading { VStack(spacing: 16) { ProgressView() Text("Generating \(itemCount) items...") } } else { QueryView() } } .task { for i in 1...itemCount { context.insert(Item(name: "Item \(i)")) } try? context.save() isLoading = false } } }

Since publishing new record types to my CloudKit schema in production, a previously unchanged record type has stopped indexing new records. While records of this type are successfully saved without errors, they are not returned in query results—they can only be accessed directly via their recordName. This issue occurs exclusively in the Production environment, both in the CloudKit Console and our iOS app. The problem began on July 21, 2025, and continues to persist. The issue affects only new records of this specific record type; all other types are indexing and querying as expected. The affected record's fields are properly configured with the appropriate index types (e.g., QUERYABLE) and have been not been modified prior to publishing the schema. With this, are there any steps I should take to restore indexing functionality for this record type in Production? There have been new records inserted, and I would prefer to not have to reset the production database, if possible.

I'm running a project with these settings: Default Actor Isolation: MainActor Approachable Concurrency: Yes Strict Concurrency Checking: Complete (this issue does not appear on the other two modes) I receive a warning for this very simple use case. Can I actually fix anything about this or is this a case of Core Data not being entirely ready for this? In reference to this, there was a workaround listed in the release notes of iOS 26 beta 5 (https://forums.swift.org/t/defaultisolation-mainactor-and-core-data-background-tasks/80569/22). Does this still apply as the only fix for this? This is a simplified sample meant to run on a background context. The issue obviously goes away if this function would just run on the MainActor, then I can remove the perform block entirely. class DataHandler { func createItem() async { let context = ... await context.perform { let newGame = Item(context: context) /// Main actor-isolated property 'timestamp' can not be mutated from a Sendable closure newGame.timestamp = Date.now // ... } } } The complete use case would be more like this: nonisolated struct DataHandler { @concurrent func saveItem() async throws { let context = await PersistenceController.shared.container.newBackgroundContext() try await context.perform { let newGame = Item(context: context) newGame.timestamp = Date.now try context.save() } } }

I’m building an app that edits files in iCloud and uses an NSFilePresenter to monitor changes. When a conflict occurs, the system calls presentedItemDidGain(_:). In that method, I merge the versions by reading the current (canonical) version using NSFileVersion.currentVersionOfItem(at:) and the conflicting ones using NSFileVersion.unresolvedConflictVersionsOfItem(at:). This generally works, but sometimes, if two devices edit the same file at the same time, each device sees its own local version as the current one. For example: Device A writes fileVerA (slightly later in real time) Device B writes fileVerB On Device A all works fine, currentVersionOfItem returns fileVerA, as expected, and unresolvedConflictVersionsOfItem returns [fileVerB]. But on Device B, currentVersionOfItem returns fileVerB!? And unresolvedConflictVersionsOfItem returns the same, local file [fileVerB], without any hint of the other conflicting version, fileVerA. Later, the newer version from the Device A arrives on Device B as a normal, non-conflicting update via presentedItemDidChange(_:). This seems to contradict Apple’s documentation: “The currentVersionOfItemAtURL: method returns an NSFileVersion object representing what’s referred to as the current file; the current file is chosen by iCloud on some basis as the current “conflict winner” and is the same across all devices.” Is this expected behavior, or a bug in how iCloud reports file versions?

Hi all, I’m encountering a consistent issue with SwiftData on watchOS when using CloudKit sync. After enabling: let config = ModelConfiguration(schema: schema, cloudKitDatabase: .automatic) …the app terminates ~30–60 seconds into a WKExtendedRuntimeSession. This happens specifically when: Always-On Display is OFF The iPhone is disconnected or in Airplane Mode The app is running in a WKExtendedRuntimeSession (e.g., used for meditation tracking) The Xcode logs show a warning: Background Task ("CoreData: CloudKit Setup"), was created over 30 seconds ago. In applications running in the background, this creates a risk of termination. It appears CloudKit sync setup is being triggered automatically and flagged by the system as an unmanaged long-running task, leading to termination. Workaround: Switching to: let config = ModelConfiguration(schema: schema, cloudKitDatabase: .none) …prevents the issue entirely — no background task warning, no crash. Feedback ID submitted: FB17685611 Just wanted to check if others have seen this behavior or found alternative solutions. It seems like something Apple may need to address in SwiftData’s CloudKit handling on watchOS.

What have people's experience with converting locally stored app data to a more browser based accessible format? Firebase seems expensive, Subabase a bit more challenging, and CloudKit too restrictive.

Hi everyone, I’m working on an offline-first iOS app using Core Data. I have a question about safe future updates: in my project, I want to be able to add new optional fields to existing Entities or even completely new Entities in future versions — but nothing else (no renaming, deleting, or type changes). Here’s how my current PersistenceController looks: import CoreData struct PersistenceController { static let shared = PersistenceController() let container: NSPersistentContainer init(inMemory: Bool = false) { container = NSPersistentContainer(name: "MyApp") if inMemory { container.persistentStoreDescriptions.first!.url = URL(fileURLWithPath: "/dev/null") } container.loadPersistentStores(completionHandler: { (storeDescription, error) in if let error = error as NSError? { print("Core Data failed to load store: \(error), \(error.userInfo)") } }) container.viewContext.automaticallyMergesChangesFromParent = true } } Do I need to explicitly set these properties to ensure lightweight migration works? shouldMigrateStoreAutomatically = true shouldInferMappingModelAutomatically = true Or, according to the documentation, are they already true by default, so I can safely add optional fields and new Entities in future versions without breaking users’ existing data? Thanks in advance for your guidance!

In an iOS App that uses CKShare I have a many-to-many relationship that does not consistently sync between the share's N participants. The relationship is between Group and Player as group.players and player.groups. As an example, given 3 group each with 4 players (aka 4:4:4), some devices show CoreData (it is NOT a UI issue) with 4:2:3 or 3:4:4. (A deletion of CoreData from a device, forcing a full re-sync from CloudKit, seems to populate the group:player relationships consistently; but obviously that is impractical to resolving the issue). How do I avoid these sync-from-CloudKit inconsistencies? Note: AI agents generally suggest adding a CoreData 'join' entity - such as 'GroupPlayer'. Is that THE fix?

I have an iOS app (1Address) which allows users to share their address with family and friends using CloudKit Sharing. Users share their address record (CKRecord) via a share link/url which when tapped allows the receiving user to accept the share and have a persistent view into the sharing user's address record (CKShare). However, most users when they recieve a sharing link do not have the app installed yet, and so when a new receiving user taps the share link, it prompts them to download the app from the app store. After the new user downloads the app from the app store and opens the app, my understanding is that the system (iOS) will/should then vend to my app the previously tapped cloudKitShareMetadata (or share url), however, this metadata is not being vended by the system. This forces the user to re-tap the share link and leads to some users thinking the app doesn't work or not completing the sharing / onboarding flow. Is there a workaround or solve for this that doesn't require the user to tap the share link a second time? In my scene delegate I am implementing: func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {...} And also func scene(_ scene: UIScene, continue userActivity: NSUserActivity) {...} And also: func windowScene(_ windowScene: UIWindowScene, userDidAcceptCloudKitShareWith cloudKitShareMetadata: CKShare.Metadata) {...} And: func scene(_ scene: UIScene, openURLContexts URLContexts: Set<UIOpenURLContext>) {...} Unfortunately, none of these are called or passed metadata on the initial app run after install. Only after the user goes back and taps a link again can they accept the share. This documentation: https://developer.apple.com/documentation/cloudkit/ckshare says that adding the CKSharingSupported key to your app's Info.plist file allows the system to launch your app when a user taps or clicks a share URL, but it does not clarify what should happen if your app is being installed for the first time. This seems to imply that the system is holding onto the share metadata and/or url, but for some reason it is not being vended to the app on first run. Open to any ideas here for how to fix and I also filed feedback: FB20934189.

There's some logic in my app that first checks to see if a specific CloudKit record zone exists. If it doesn't, it creates the zone, and then my application continues on with its work. The way I've implemented this right now is by catching the zoneNotFound error when I call CKDatabase#recordZone(for:) (docs) and creating the zone when that happens: do { try await db.recordZone(for: zoneID) } catch let ckError as CKError where [.zoneNotFound, .userDeletedZone].contains(ckError.code) { // createZone is a helper function try await createZone(zoneID: zoneID, context: context) } This works great, but every time I do this, an error is logged in CloudKit Console, which creates a lot of noise and makes it harder to see real errors. Is there a way to do this without explicitly triggering a CloudKit error? I just found CKDatabase#recordZones(for:) (docs), which seems like it returns an empty array instead of throwing an error if the zone doesn't exist. Will calling that and looking for a non-empty array work just as well, but without logging lots of errors in the console?

I encountered an error when trying to rollback context after deleting some model with multiple one-to-many relationships when encountered a problem later in a deleting method and before saving the changes. Something like this: do { // Fetch model modelContext.delete(model) // Do some async work that potentially throws try modelContext.save() } catch { modelContext.rollback() } When relationship is empty - the parent has no children - I can safely delete and rollback with no issues. However, when there is even one child when I call even this code: modelContext.delete(someModel) modelContext.rollback() I'm getting a fatal error: SwiftData/ModelSnapshot.swift:46: Fatal error: Unexpected backing data for snapshot creation: SwiftData._FullFutureBackingData<ChildModel> I use ModelContext from within the ModelActor but using mainContext changes nothing. My ModelContainer is quite simple and problem occurs on both in-memory and persistent storage, with or without CloudKit database being enabled. I can isolate the issue in test environment, so the model that's being deleted (or any other) is not being accessed by any other part of the application. However, problem looks the same in the real app. I also changed the target version of iOS from 18.0 to 26.0, but to no avail. My models look kind of like this: @Model final class ParentModel { var name: String @Relationship(deleteRule: .cascade, inverse: \ChildModel.parent) var children: [ChildModel]? init(name: String) { self.name = name } } @Model final class ChildModel { var name: String @Relationship(deleteRule: .nullify) var parent: ParentModel? init(name: String) { self.name = name } } I tried many approaches that didn't help: Fetching all children (via fetch) just to "populate" the context Accessing all children on parent model (via let _ = parentModel.children?.count) Deleting all children reading models from parent: for child in parentModel.children ?? [] { modelContext.delete(child) } Deleting all children like this: let parentPersistentModelID = parentModel.persistentModelID modelContext.delete(model: ChildModel.self, where: #Predicate { $0.parent.persistentModelID == parentPersistentModelID }, includeSubclasses: true) Removing @Relationship(deleteRule: .nullify) from ChildModel relationship definition I found 2 solution for the problem: To manually fetch and delete all children prior to deleting parent: let parentPersistentModelID = parentModel.persistentModelID for child in try modelContext.fetch(FetchDescriptor<ChildModel>(predicate: #Predicate { $0.parent.persistentModelID == parentPersistentModelID })) { modelContext.delete(child) } modelContext.delete(parentModel) Trying to run my code in child context (let childContext = ModelContext(modelContext.container)) All that sounds to me like a problem deep inside Swift Data itself. The first solution I found, fetching potentially hundreds of child models just to delete them in case I might need to rollback changes on some error, sounds like awful waste of resources to me. The second one however seems to work fine has that drawback that I can't fully test my code. Right now I can wrap the context (literally creating class that holds ModelContext and calls its methods) and in tests for throwing methods force them to throw. By creating scratch ModelContext I loose that possibility. What might be the real issue here? Am I missing something?

I have a single multiplatform application that I use NSPersistentCloudKitContainer on. This works great, except I noticed when I open two instances of the same process (not windows) on the same computer, which share the same store, data duplication and "Metadata Inconsistency" errors start appearing. This answer (https://stackoverflow.com/a/67243833) says this is not supported with NSPersistentCloudKitContainer. Is this indeed true? If it isn't allowed, is the only solution to disable multiple instances of the process via a lock file? I was thinking one could somehow coordinate a single "leader" process that syncs to the cloud, with the others using NSPersistentContainer, but this would be complicated when the "leader" process terminates. Currently, it seems iPad split views are new windows, not processes -- but overall I'm still curious :0 Thank you!

The following complex migration consistently crashes the app with the following error: SwiftData/PersistentModel.swift:726: Fatal error: What kind of backing data is this? SwiftData._KKMDBackingData<SwiftDataMigration.ItemSchemaV1.ItemList> My app relies on a complex migration that involves these optional 1 to n relationships. Theoretically I could not assign the relationships in the willMigrate block but afterwards I am not able to tell which list and items belonged together. Steps to reproduce: Run project Change typealias CurrentSchema to ItemSchemaV2 instead of ItemSchemaV1. Run project again -> App crashes My setup: Xcode Version 16.2 (16C5032a) MacOS Sequoia 15.4 iPhone 12 with 18.3.2 (22D82) Am I doing something wrong or did I stumble upon a bug? I have a demo Xcode project ready but I could not upload it here so I put the code below. Thanks for your help typealias CurrentSchema = ItemSchemaV1 typealias ItemList = CurrentSchema.ItemList typealias Item = CurrentSchema.Item @main struct SwiftDataMigrationApp: App { var sharedModelContainer: ModelContainer = { do { return try ModelContainer(for: ItemList.self, migrationPlan: MigrationPlan.self) } catch { fatalError("Could not create ModelContainer: \(error)") } }() var body: some Scene { WindowGroup { ContentView() } .modelContainer(sharedModelContainer) } } This is the migration plan enum MigrationPlan: SchemaMigrationPlan { static var schemas: [any VersionedSchema.Type] { [ItemSchemaV1.self, ItemSchemaV2.self] } static var stages: [MigrationStage] = [ MigrationStage.custom(fromVersion: ItemSchemaV1.self, toVersion: ItemSchemaV2.self, willMigrate: { context in print("Started migration") let oldlistItems = try context.fetch(FetchDescriptor<ItemSchemaV1.ItemList>()) for list in oldlistItems { let items = list.items.map { ItemSchemaV2.Item(timestamp: $0.timestamp)} let newList = ItemSchemaV2.ItemList(items: items, name: list.name, note: "This is a new property") context.insert(newList) context.delete(list) } try context.save() // Crash indicated here print("Finished willMigrate") }, didMigrate: { context in print("Did migrate successfully") }) ] } The versioned schemas enum ItemSchemaV1: VersionedSchema { static var versionIdentifier = Schema.Version(1, 0, 0) static var models: [any PersistentModel.Type] { [Item.self] } @Model final class Item { var timestamp: Date var list: ItemSchemaV1.ItemList? init(timestamp: Date) { self.timestamp = timestamp } } @Model final class ItemList { @Relationship(deleteRule: .cascade, inverse: \ItemSchemaV1.Item.list) var items: [Item] var name: String init(items: [Item], name: String) { self.items = items self.name = name } } } enum ItemSchemaV2: VersionedSchema { static var versionIdentifier = Schema.Version(2, 0, 0) static var models: [any PersistentModel.Type] { [Item.self] } @Model final class Item { var timestamp: Date var list: ItemSchemaV2.ItemList? init(timestamp: Date) { self.timestamp = timestamp } } @Model final class ItemList { @Relationship(deleteRule: .cascade, inverse: \ItemSchemaV2.Item.list) var items: [Item] var name: String var note: String init(items: [Item], name: String, note: String = "") { self.items = items self.name = name self.note = note } } } Last the ContentView: struct ContentView: View { @Query private var itemLists: [ItemList] var body: some View { NavigationSplitView { List { ForEach(itemLists) { list in NavigationLink { List(list.items) { item in Text(item.timestamp.formatted(date: .abbreviated, time: .complete)) } .navigationTitle(list.name) } label: { Text(list.name) } } } .navigationTitle("Crashing migration demo") .onAppear { if itemLists.isEmpty { for index in 0..<10 { let items = [Item(timestamp: Date.now)] let listItem = ItemList(items: items, name: "List No. \(index)") modelContext.insert(listItem) } try! modelContext.save() } } } detail: { Text("Select an item") } } }

Hi, I was testing the new iOS 18 behavior where NSPersistentCloudKitContainer wipes the local Core Data store if the user logs out of iCloud, for privacy purposes. I ran the tests both with a Core Data + CloudKit app, and a simple one using SwiftData with CloudKit enabled. Results were identical in either case. In my testing, most of the time, the feature worked as expected. When I disabled iCloud for my app, the data was wiped (consistent with say the Notes app, except if you disable iCloud it warns you that it'll remove those notes). When I re-enabled iCloud, the data appeared. (all done through the Settings app) However, in scenarios when NSPersistentCloudKitContainer cannot immediately sync -- say due to rate throttling -- and one disables iCloud in Settings, this wipes the local data store and ultimately results in data loss. This occurs even if the changes to the managed objects are saved (to the local store) -- it's simply they aren't synced in time. It can be a little hard to reproduce the issue, especially since when you exit to the home screen from the app, it generally triggers a sync. To avoid this, I swiped up to the screen where you can choose which apps to close, and immediately closed mine. Then, you can disable iCloud, and run the app again (with a debugger is helpful). I once saw a message with something along the lines of export failed (for my record that wasn't synced), and unfortunately it was deleted (and never synced). Perhaps before NSPersistentCloudKitContainer wipes the local store it ought to force sync with the cloud first?

Hello Apple Team, We’re building a CloudKit-enabled Core Data app and would like clarification on the behavior and performance characteristics of Binary Data attributes with “Allows External Storage” enabled when used with NSPersistentCloudKitContainer. Initially, we tried storing image files manually on disk and only saving the metadata (file URLs, dimensions, etc.) in Core Data. While this approach reduced the size of the Core Data store, it introduced instability after app updates and broke sync between devices. We would prefer to use the official Apple-recommended method and have Core Data manage image storage and CloudKit syncing natively. Specifically, we’d appreciate guidance on the following: When a Binary Data attribute is marked as “Allows External Storage”, large image files are stored as separate files on device rather than inline in the SQLite store. How effective is this mechanism in keeping the Core Data store size small on device? Are there any recommended size thresholds or known limits for how many externally stored blobs can safely be managed this way? How are these externally stored files handled during CloudKit sync? Does each externally stored Binary Data attribute get mirrored to CloudKit as a CKAsset? Does external storage reduce the sync payload size or network usage, or is the full binary data still uploaded/downloaded as part of the CKAsset? Are there any bandwidth implications for users syncing via their private CloudKit database, versus developer costs in the public CloudKit database? Is there any difference in CloudKit or Core Data behavior when a Binary Data attribute is managed this way versus manually storing image URLs and handling the file separately on disk? Our goal is to store user-generated images efficiently and safely sync them via CloudKit, without incurring excessive local database bloat or CloudKit network overhead. Any detailed guidance or internal performance considerations would be greatly appreciated. Thank you, Paul Barry Founder & Lead Developer — Boat Buddy / Vessel Buddy iOS App Archipelago Environmental Solutions Inc.

My iOS app uses CloudKit key-value storage. I have not updated the app in a few years but it works fine. Since it was last updated, I transferred the app from an old organization to my personal developer account. Now that I'm working on the app again I get an error: Provisioning profile "iOS Team Provisioning Profile: com.company.app" doesn't match the entitlements file's value for the com.apple.developer.ubiquity-kvstore-identifier entitlement. In the entitlement file, it has $(TeamIdentifierPrefix)$(CFBundleIdentifier) as the value for iCloud Key-Value Store. I've verified the variables resolve as expected. When I parse the provisioning profile there is no entitlement value for key-value storage. What am I getting wrong?

When my app starts it loads data (of vehicle models, manufacturers, ...) from JSON files into CoreData.  This content is static. Some CoreData entities have fields that can be set by the user, for example an isFavorite boolean field. How do I tell CloudKit that my CoreData objects are 'static' and must not be duplicated on other devices (that will also load it from JSON files). In other words, how can I make sure that the CloudKit knows that the record created from JSON for vehicle model XYZ on one device is the same record that was created from JSON on any other device? I'm using NSPersistentCloudKitContainer.