Environment visionOS 26 Xcode 26 Issue I am experiencing crash when trying to access a [String] from a @Model data, after dismissing an immersiveSpace and opening a WindowGroup. This crash only occurs when trying to access the [String] property of my Model. It works fine with other properties. Thread 1: Fatal error: This backing data was detached from a context without resolving attribute faults: PersistentIdentifier(...) Steps to Reproduce Open WindowGroup Dismiss window, open ImmersiveSpace Dismiss ImmersiveSpace, reopen WindowGroup Any guidance would be appreciated! @main struct MyApp: App { var body: some Scene { WindowGroup(id: "main") { ContentView() } .modelContainer(for: [Item.self]) ImmersiveSpace(id: "immersive") { ImmersiveView() } } } // In SwiftData model @Model class Item { var title: String = "" // Accessing this property works fine var tags: [String] = [] @storageRestrictions(accesses: _$backingData, initializes: _tags) init(initialValue) { _$backingData.setValue(forKey: \. tags, to: initialValue) _tags =_ SwiftDataNoType() } get { _$observationRegistrar.access(self, keyPath: \.tags) **return self getValue(forkey: \.tags)** // Crashes here }

Hi everyone, I’ve been working on migrating my app (SwimTimes, which helps swimmers track their times) to use Core Data + CKSyncEngine with Swift 6. After many iterations, forum searches, and experimentation, I’ve created a focused sample project that demonstrates the architecture I’m using. The good news: 👉 I believe the crashes I was experiencing are now solved, and the sync behavior is working correctly. 👉 The demo project compiles and runs cleanly with Swift 6. However, before adopting this as the final architecture, I’d like to ask the community (and hopefully Apple engineers) to validate a few critical points, especially regarding Swift 6 concurrency and Core Data contexts. Architecture Overview Persistence layer: Persistence.swift sets up the Core Data stack with a main viewContext and a background context for CKSyncEngine. Repositories: All Core Data access is abstracted into repository classes (UsersRepository, SwimTimesRepository), with async/await methods. SyncEngine: Wraps CKSyncEngine, handles system fields, sync tokens, and bridging between Core Data entities and CloudKit records. ViewModels: Marked @MainActor, exposing @Published arrays for SwiftUI. They never touch Core Data directly, only via repositories. UI: Simple SwiftUI views bound to the ViewModels. Entities: UserEntity → represents swimmers. SwimTimeEntity → times linked to a user (1-to-many). Current Status The project works and syncs across devices. But there are two open concerns I’d like validated: Concurrency & Memory Safety Am I correctly separating viewContext (main/UI) vs. background context (used by CKSyncEngine)? Could there still be hidden risks of race conditions or memory crashes that I’m not catching? Swift 6 Sendable Compliance Currently, I still need @unchecked Sendable in the SyncEngine and repository layers. What is the recommended way to fully remove these workarounds and make the code safe under Swift 6’s stricter concurrency rules? Request Please review this sample project and confirm whether the concurrency model is correct. Suggest how I can remove the @unchecked Sendable annotations safely. Any additional code improvements or best practices would also be very welcome — the intention is to share this as a community resource. I believe once finalized, this could serve as a good reference demo for Core Data + CKSyncEngine + Swift 6, helping others migrate safely. Environment iOS 18.5 Xcode 16.4 macOS 15.6 Swift 6 Sample Project Here is the full sample project on GitHub: 👉 [https://github.com/jarnaez728/coredata-cksyncengine-swift6] Thanks a lot for your time and for any insights! Best regards, Javier Arnáez de Pedro

I have made a Swift App for MacOS 15 under XCode 16.3, which runs fine. I also want to run it under the previous MacOS 14. Unfortunately it crashes without even starting up (it does not even reach the first log output statement on the first view) The crash reason is Crashed Thread: 0 Dispatch queue: com.apple.main-thread Exception Type: EXC_BAD_INSTRUCTION (SIGILL) Exception Codes: 0x0000000000000001, 0x0000000000000000 Termination Reason: Namespace SIGNAL, Code 4 Illegal instruction: 4 Terminating Process: exc handler [2970] I have set the miminium deployment to MacOS 14.0 but to no effect. The XCode machine is a MacOS 15.4 on Arm M3 and the target machine is MacOS 14.7.5 on Intel (MacBook Air) I think it might be related to the compiler and linker settings.

hi, in my app, i have created and pushed CKRecords to the public database. others using the app have pushed CKRecords as well. is there any way i can query iCloud for "all the CKRecords that i created?" thanks, DMG

Hi, I keep trying to use transformable to store an array of strings with SwiftData, and I can see that it is activating the transformer, but it keeps saying that I am still using NSArray instead of NSData. *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Unacceptable type of value for attribute: property = "category"; desired type = NSData; given type = Swift.__SwiftDeferredNSArray; value = ( yo, gurt ).' terminating due to uncaught exception of type NSException CoreSimulator 1010.10 - Device: iPhone 16 18.0 (6879535B-3174-4025-AD37-ED06E60291AD) - Runtime: iOS 18.0 (22A3351) - DeviceType: iPhone 16 Message from debugger: killed @Model class MyModel: Identifiable, Equatable { @Attribute(.transformable(by: StringArrayTransformer.self)) var category: [String]? @Attribute(.transformable(by: StringArrayTransformer.self)) var amenities: [String]? var image: String? var parentChunck: HenricoPostDataChunk_V1? init(category: [String]?, amenities: [String]?) { self.category = category self.amenities = amenities } } class StringArrayTransformer: ValueTransformer { override func transformedValue(_ value: Any?) -> Any? { print(value) guard let array = value as? [String] else { return nil } let data = try? JSONSerialization.data(withJSONObject: array, options: []) print(data) return data } override func reverseTransformedValue(_ value: Any?) -> Any? { guard let data = value as? Data else { return nil } let string = (try? JSONSerialization.jsonObject(with: data, options: [])) as? [String] print(string) return string } override class func transformedValueClass() -> AnyClass { return NSData.self } override class func allowsReverseTransformation() -> Bool { return true } static func register() { print("regitsering") ValueTransformer.setValueTransformer(StringArrayTransformer(), forName: .stringArrayTransformerName) } } extension NSValueTransformerName { static let stringArrayTransformerName = NSValueTransformerName("StringArrayTransformer") }

I have an app that from day 1 has used Swiftdata and successfully sync'd across devices with Cloudkit. I have added models to the data in the past and deployed the schema and it continued to sync across devices. Sometime I think in June.2025 I added a new model and built out the UI to display and manage it. I pushed a version to Test Flight (twice over a matter of 2 versions and a couple of weeks) and created objects in the new model in Test Flight versions of the app which should push the info to Cloudkit to update the schema. When I go to deploy the schema though there are no changes. I confirmed in the app that Cloudkit is selected and it's point to the correct container. And when I look in Cloudkit the new model isn't listed as an indes. I've pushed deploy schema changes anyway (more than once) and now the app isn't sync-ing across devices at all (even the pre-existing models aren't sync-ing across devices). I even submitted the first updated version to the app store and it was approved and released. I created objects in the new model in production which I know doesn't create the indexes in the development environment. But this new model functions literally everywhere except Cloudkit and I don't know what else to do to trigger an update.

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, In my iOS/SwiftUI/SwiftData app, I want the user to be able to hit [Cancel] from editing in a detail screen and return to the previous screen without changes being saved. I believed that setting autosaveEnabled to false and/or calling .rollback would prevent changes from being saved, unless/until I call .save() when the user clicks [Save], but this does not seem to be correct. I set modelContext.autosaveEnabled = false and I call modelContext.rollback() when the user hits [Cancel], but any changes they made are not rolled back, but saved even if I don’t call save(). I have tried setting autosaveEnabled to false when I create the ModelContainer on a @MainActor function when the App starts, and in the detail/edit screen’s .onAppear(). I can see that .rollback is being called when the [Cancel] button is tapped. In all cases, any changes the user made before hitting [Cancel] are saved. The Developer Documentation on autosaveEnabled includes this: “The default value is false. SwiftData automatically sets this property to true for the model container’s mainContext." I am working on the mainContext, but it appears that setting autosaveEnabled to false has no effect no matter where in the code I set it. If someone sees what I am doing wrong, I’d sure appreciate the input. If this description doesn’t explain the problem well enough, I’ll develop a minimal focused example.

Hi, Before the iOS 17.2 update the saving behavior of SwiftData was very straightforward, by default it saves to persistence storage and can be configured to save in memory only. Now it saves to memory by default and to make it save to persistence storage we need to use modelContext.Save(). But if we don't quit the App the changes will be saved after a while to persistence storage even without running modelContext.Save() ! How confusing can that be for both developer and the user ! Am I missing something here ? -- Kind Regards

Hi, I’m running into an issue with Core Data migrations using a custom NSMappingModel created entirely in Swift (not using .xcmappingmodel files). Setup: • I’m performing a migration with a manually constructed NSMappingModel • One of the NSEntityMapping instances is configured as follows: • mappingType = .customEntityMappingType (or .transformEntityMappingType) • entityMigrationPolicyClassName is set to a valid subclass of NSEntityMigrationPolicy • The class implements the expected methods like: @objc func createDestinationInstances(…) throws { … } @objc func createCustomDestinationInstance(…) throws -> NSManagedObject { … } The policy class is instantiated (confirmed via logging in init()), but none of the migration methods are ever called. I have also tried adding valid NSPropertyMapping instances with real valueExpression bindings to force activation, but that didn’t make a difference. Constraints: • I cannot use .xcmappingmodel files in this context due to transformable attributes not compatible with the visual editor. • Therefore, I need the entire mapping model to be defined in Swift. Workaround: As a temporary workaround, I’m migrating the data manually using two persistent stores and NSManagedObjectContext, but I’d prefer to rely on NSMigrationManager as designed. Question: Is there a known limitation that prevents Core Data from invoking NSMigrationPolicy methods when using in-memory NSMappingModel instances? Or is there any specific setup required to trigger them when not loading from .xcmappingmodel? Thanks in advance.

I am working on a SwiftUI project using Core Data. I have an entity called AppleUser in my data model, with the following attributes: id (UUID), name (String), email (String), password (String), and createdAt (Date). All attributes are non-optional. I created the corresponding Core Data class files (AppleUser+CoreDataClass.swift and AppleUser+CoreDataProperties.swift) using Xcode’s automatic generation. I also have a PersistenceController that initializes the NSPersistentContainer with the model name JobLinkModel. When I try to save a new AppleUser object using: let user = AppleUser(context: viewContext) user.id = UUID() user.name = "User1" user.email = "..." user.password = "password1" user.createdAt = Date()【The email is correctly formatted, but it has been replaced with “…” for privacy reasons】 try? viewContext.save() I get the following error in the console:Core Data save failed: Foundation._GenericObjCError.nilError, [:] User snapshot: ["id": ..., "name": "User1", "email": "...", "password": "...", "createdAt": ...] All fields have valid values, and the Core Data model seems correct. I have also tried: • Checking that the model name in NSPersistentContainer(name:) matches the .xcdatamodeld file (JobLinkModel) • Ensuring the AppleUser entity Class, Module, and Codegen are correctly set (Class Definition, Current Product Module) • Deleting duplicate or old AppleUser class files • Cleaning Xcode build folder and deleting the app from the simulator • Using @Environment(.managedObjectContext) for the context Despite all this, I still get _GenericObjCError.nilError when saving a new AppleUser object. I want to understand: 1. Why is Core Data failing to save even though all fields are non-nil and correctly assigned? 2. Could this be caused by some residual old class files, or is there something else in the setup that I am missing? 3. What steps should I take to ensure that Core Data properly recognizes the AppleUser entity and allows saving? Any help or guidance would be greatly appreciated.

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.

it seems that is going to the appstore to find the app to execute the share but my app is not in the appstore yet. I am using a sandboxed user and a non sandboxed user, I have tried real phones connected to xcode and simulator same effect, looking for how to test my ckshare in testflight thanks

I have been using the basic NSPersistentContainer with 100k+ records for a while now with no issues. The database size can fluctuate a bit but on average it takes up about 22mb on device. When I switch the container to NSPersistentCloudKitContainer, I see a massive increase in size to ~150mb initially. As the sync engine uploads records to iCloud it has ballooned to over 600mb on device. On top of that, the user's iCloud usage in settings reports that it takes up 1.7gb in the cloud. I understand new tables are added and history tracking is enabled but the size increase seems a bit drastic. I'm not sure how we got from 22mb to 1.7gb with the exact same data. A few other things that are important to note: I import all the 100k+ records at once when testing the different containers. At the time of the initial import there is only 1 relation (an import group record) that all the records are attached to. I save the background context only once after all the records and the import group have been made and added to the context. After the initial import, some of these records may have a few new relations added to them over time. I suppose this could be causing some of the size increase, but its only about 20,000 records that are updated. None of the records include files/ large binary data. Most of the attributes are encrypted. I'm syncing to the dev iCloud environment. When I do make a change to a single attribute in a record, CloudKit reports that every attribute has been modified (not sure if this is normal or not ) Also, When syncing to a new device, the sync can take hours - days. I'm guessing it's having to sync both the new records and the changes, but it exponentially gets slower as more records are downloaded. The console will show syncing activity, but new records are being added at a slower rate as more records are added. After about 50k records, it grinds to a halt and while the console still shows sync activity, only about 100 records are added every hour. All this to say i'm very confused where these issues are coming from. I'm sure its a combination of how i've setup my code and the vast record count, record history, etc. If anyone has any ideas it would be much appreciated.

When I used to do Migrations, I always used ETL and then push to a dev system to review/test before going production. The migration support is SwiftData is fine for a little tweak. I might as well just just use new schema and context and write the custom code than use the SwiftData migration support.

I'm trying to set up an application using SwiftData to have a number of models backed by a local datastore that's not synced to CloudKit, and another set of models that is. I was able to achieve this previously with Core Data using multiple NSPersistentStoreDescription instances. The set up code looks something like: do { let fullSchema = Schema([ UnsyncedModel.self, SyncedModel.self, ]) let localSchema = Schema([UnsyncedModel.self]) let localConfig = ModelConfiguration(schema: localSchema, cloudKitDatabase: .none) let remoteSchema = Schema([SyncedModel.self]) let remoteConfig = ModelConfiguration(schema: remoteSchema, cloudKitDatabase: .automatic) container = try ModelContainer(for: fullSchema, configurations: localConfig, remoteConfig) } catch { fatalError("Failed to configure SwiftData container.") } However, it doesn't seem to work as expected. If I remove the synced/remote schema and configuration then everything works fine, but the moment I add in the remote schema and configuration I get various different application crashes. Some examples below: A Core Data error occurred." UserInfo={Reason=Entity named:... not found for relationship named:..., Fatal error: Failed to identify a store that can hold instances of SwiftData._KKMDBackingData<...> Has anyone ever been able to get a similar setup to work using SwiftData?

Hi guys. Can someone please confirm this bug so I report it? The issue is that SwiftData relationships don't update the views in some specific situations on devices running iOS 18 Beta. One clear example is with CloudKit. I created a small example for testing. The following code creates two @models, one to store bands and another to store their records. The following code works with no issues. (You need to connect to a CloudKit container and test it on two devices) import SwiftUI import SwiftData struct ContentView: View { @Environment(\.modelContext) private var modelContext @Query private var records: [Record] var body: some View { NavigationStack { List(records) { record in VStack(alignment: .leading) { Text(record.title) Text(record.band?.name ?? "Undefined") } } .toolbar { ToolbarItem { Button("Add Record") { let randomNumber = Int.random(in: 1...100) let newBand = Band(name: "New Band \(randomNumber)", records: nil) modelContext.insert(newBand) let newRecord = Record(title: "New Record \(randomNumber)", band: newBand) modelContext.insert(newRecord) } } } } } } @Model final class Record { var title: String = "" var band: Band? init(title: String, band: Band?) { self.title = title self.band = band } } @Model final class Band { var name: String = "" var records: [Record]? init(name: String, records: [Record]?) { self.name = name self.records = records } } This view includes a button at the top to add a new record associated with a new band. The data appears on both devices, but if you include more views inside the List, the views on the second device are not updated to show the values of the relationships. For example, if you extract the row to a separate view, the second device shows the relationships as "Undefined". You can try the following code. struct ContentView: View { @Environment(\.modelContext) private var modelContext @Query private var records: [Record] var body: some View { NavigationStack { List { ForEach(records) { record in RecordRow(record: record) } } .toolbar { ToolbarItem { Button("Add Record") { let randomNumber = Int.random(in: 1...100) let newBand = Band(name: "New Band \(randomNumber)", records: nil) modelContext.insert(newBand) let newRecord = Record(title: "New Record \(randomNumber)", band: newBand) modelContext.insert(newRecord) } } } } } } struct RecordRow: View { let record: Record var body: some View { VStack(alignment: .leading) { Text(record.title) Text(record.band?.name ?? "Undefined") } } } Here I use a ForEach loop and move the row to a separate view. Now on the second device the relationships are nil, so the row shows the text "Undefined" instead of the name of the band. I attached an image from my iPad. I inserted all the information on my iPhone. The first three rows were inserted with the first view. But the last two rows were inserted after I extracted the rows to a separate view. Here you can see that the relationships are nil and therefore shown as "Undefined". The views are not updated to show the real value of the relationship. This example shows the issue with CloudKit, but this also happens locally in some situations. The system doesn't detect updates in relationships and therefore doesn't refresh the views. Please, let me know if you can reproduce the issue. I'm using Mac Sequoia 15.1, and two devices with iOS 18.0.

I have a new app I am working on, it uses, a container id like com.me.mycompany.FancyApp.prod, the description in the app is My Fancy App. When I deploy the app via TestFlight on a real device, the sync seems to work, but when I view iCloud->Storage-List, I see my app icon, and the name "prod". Where did the name prod come from? It should be My Fancy App, which is the actual name of the App.

I'm seeing this over and over on the CloudKit Console at: https://icloud.developer.apple.com/dashboard/home, and sign out and sign in does not resolve it. Error looking up Developer Teams Please sign out and try again. [Sign Out] Anyone experience this? Is there a work around for this?

Hello there, I have a problem reaching the CloudKit dashboard. Every time I login, the login successes but then I get the error: An error has caused this web page to stop working correctly. This also happens when I click on the Button CloudKit dashboard. Then I can reload the page, but the same errors occurs again and again. Can someone help me with this problem? Thank you very much