Hi everyone, We’re currently using CKSyncEngine to sync all our locally persisted data across user devices (iOS and macOS) via iCloud. We’ve noticed something strange and reproducible: On iOS, when the CKSyncEngine is initialized with manual sync behavior, both manual calls to fetchChanges() and sendChanges() happen nearly instantly (usually within seconds). Automatic syncing is also very fast. On macOS, when the CKSyncEngine is initialized with manual sync behavior, fetchChanges() and sendChanges() are also fast and responsive. However, once CKSyncEngine is initialized with automatic syncing enabled on macOS: sendChanges() still appears to transmit changes immediately. But automatic fetching becomes significantly slower — often taking minutes to pick up changes from the cloud, even when new data is already available. Even manual calls to fetchChanges() behave as if they’re throttled or delayed, rather than performing an immediate fetch. Our questions: Is this delay in automatic (and post-automatic manual) fetch behavior on macOS expected, or possibly a bug? Are there specific macOS constraints that impact CKSyncEngine differently than on iOS? Once CKSyncEngine has been initialized in automatic mode, is fetchChanges() no longer treated as a truly manual trigger? Is there a recommended workaround to enable fast sync behavior on macOS — for example, by sticking to manual sync configuration and triggering sync using a CKSubscription-based mechanism when remote changes occur? Any guidance, clarification, or experiences from other developers (or Apple engineers) would be greatly appreciated — especially regarding maintaining parity between iOS and macOS sync performance. Thanks in advance!

For a CRM application, I want users to be able to switch between accounts and have their saved contacts stored locally. Whenever a user logs in, the app should fetch data from their specific database location. What’s the best practice to achieve this? Should I create a separate database for each user? Should I store all the data in one database and filter it by user? Or is there a better approach I should consider?

I have one target building and filling the SwiftData store and then copying the same store file to another target of the app to use the contents. That worked fine from iOS 17 to iOS 26.0.1 Under iOS 26.1 I am getting following error: CoreData: error: This store file was previously used on a build with Persistence-1522 but is now running on a build with Persistence-1518. file:///Users/xxx/Library/Developer/CoreSimulator/Devices/0FE92EA2-57FA-4A5E-ABD0-DAB4DABC3E02/data/Containers/Data/Application/B44D3256-9B09-4A60-94E2-C5F11A6519E7/Documents/default.store What does it mean and how to get back to working app under iOS 26.1?

Hi, I'm using SwiftData in my app, and I want to sent data to iCloud with CloudKit, but I found that If the user turns off my App iCloud sync function in the settings App, the local data will also be deleted. A better way is maintaining the local data, just don't connect to iCloud.How should I do that? I need guidance!!! I'm just getting started with CloudKit And I would be appreciated!

In the future, is there any plans to have AppMigrationKit for macOS-Windows cross transfers (or Linux, ChromeOS, HarmonyOS NEXT, etc)? Additionally, will the migration framework remain just iOS <-> Android or will it extend to Windows tablets, ChromeOS Tablets, HarmonyOS NEXT, KaiOS, Series 30+, Linux mobile, etc.

I have been trying to find out the app limits to my app when released into the app store, I understand that in the public database the app worldwide can use 200g of bandwidth free per month. What happens after that? is it throttled? is there a pricing structure for overages? thanks

What is the idiomatic way to use a ModelContext in a document based SwiftData app from a background thread? The relevant DocumentGroup initializers do not give us direct access to a ModelContainer, only to a ModelContext. Is it safe to take its modelContext.container and pass it around (for creating a ModelContext on it on a background thread) or to construct a ModelActor with it? Is it safe to e.g. put a ModelActor so created into the environment of the root view of the window and execute various async data operations on it in Tasks throughout the app, as long as these are dispatched from within the window whose root view's ModelContext was used for getting the ModelContainer?

"No records found" If I create a new record on the console, I can copy the record name. I can then query for recordName and get that individual record back. BUT no other queries work. I cannot query all records. I cannot query by individual property. Just returns "no records found" Seems like my indexes got messed up. Is there a way to reset indexes on prod? This is on a coredata.cloudkit managed zone.

Hello, I tried to validate if my app was properly syncing to the cloud. To test this, I created some data in the app, and then deleted the app, and reinstalled. I was expecting the data to still exist but it isn't. Is this a valid test or is the data expected to be deleted when app is deleted?

I am having problems when I first loads the app. The time it takes for the Items to be sync from my CloudKit to my local CoreData is too long. Code I have the model below defined by my CoreData. public extension Item { @nonobjc class func fetchRequest() -> NSFetchRequest<Item> { NSFetchRequest<Item>(entityName: "Item") } @NSManaged var createdAt: Date? @NSManaged var id: UUID? @NSManaged var image: Data? @NSManaged var usdz: Data? @NSManaged var characteristics: NSSet? @NSManaged var parent: SomeParent? } image and usdz columns are both marked as BinaryData and Attribute Allows External Storage is also selected. I made a Few tests loading the data when the app is downloaded for the first time. I am loading on my view using the below code: @FetchRequest( sortDescriptors: [NSSortDescriptor(keyPath: \Item.createdAt, ascending: true)] ) private var items: FetchedResults<Item> var body: some View { VStack { ScrollView(.vertical, showsIndicators: false) { LazyVGrid(columns: columns, spacing: 40) { ForEach(items, id: \.self) { item in Text(item.id) } } } } } Test 1 - Just loads everything When I have on my cloudKit images and usdz a total of 100mb data, it takes around 140 seconds to show some data on my view (Not all items were sync, that takes much longer time) Test 2 - Trying getting only 10 items at the time () This takes the same amount of times the long one . I have added the following in my class, and removed the @FetchRequest: @State private var items: [Item] = [] // CK @State private var isLoading = false @MainActor func loadMoreData() { guard !isLoading else { return } isLoading = true let fetchRequest = NSFetchRequest<Item>(entityName: "Item") fetchRequest.predicate = NSPredicate(format: "title != nil AND title != ''") fetchRequest.fetchLimit = 10 fetchRequest.fetchOffset = items.count fetchRequest.predicate = getPredicate() fetchRequest.sortDescriptors = [NSSortDescriptor(keyPath: \Item.createdAt, ascending: true)] do { let newItems = try viewContext.fetch(fetchRequest) DispatchQueue.main.async { items.append(contentsOf: newItems) isLoading = false } } catch {} } Test 2 - Remove all images and usdz from CloudKit set all as Null Setting all items BinaryData to null, it takes around 8 seconds to Show the list. So as we can see here, all the solutions that I found are bad. I just wanna go to my CloudKit and fetch the data with my CoreData. And if possible to NOT fetch all the data because that would be not possible (imagine the future with 10 or 20GB or data) What is the solution for this loading problem? What do I need to do/fix in order to load lets say 10 items first, then later on the other items and let the user have a seamlessly experience? Questions What are the solutions I have when the user first loads the app? How to force CoreData to query directly cloudKit? Does CoreData + CloudKit + NSPersistentCloudKitContainer will download the whole CloudKit database in my local, is that good???? Storing images as BinaryData with Allow external Storage does not seems to be working well, because it is downloading the image even without the need for the image right now, how should I store the Binary data or Images in this case?

I am trying to test using Testflight and have set up a test with a user on an account I also own which is different to me developer account. The app I believe is running in production on a separate device and is working from a user point of view, however I am not able to query the data via the console. As I said I know the user id and password as tey are mine so even when I use the Act as user service it logs in but the query is empty. I'm assuming I'm not doing anything wrong its possibly an security issue that is preventing me accessing this account. My question to the group then is how do I verify the data that is being tested?

Hello, In our app, we’ve modeled our schema using inheritance introduced in iOS 26.0, and we’re implementing SwiftData History to re-fetch models only when necessary. @Model public class Transaction { @Attribute(.preserveValueOnDeletion) public var date: Date = Date() public var amount: Double = 0 public var memo: String? } @Model public final class Spending: Transaction { public var installmentIndex: Int = 1 public var installment: Int = 1 public var installmentID: UUID? } If data has been deleted from database, we need to check a date property to determine whether to re-fetch datas. To do this, we added the preserveValueOnDeletion attribute to date property so we could retrieve it from the History tombstone value. However, after adding this attribute, a crash occurs. There is a console log Could not cast value of type 'Swift.ReferenceWritableKeyPath<Shared.ModelSchemaV5.Transaction, Foundation.Date>' (0x106bf8328) to 'Swift.PartialKeyPath<Shared.ModelSchemaV5.Spending>' (0x1094f21d8). and error log attached StrictMoneyChecking-2025-11-07-105108.txt I also tried this in the recent SampleTrip app, and fetching all history after a deletion causes the same crash. Is this issue currently being worked on or under investigation?

I'm implementing SwiftData with inheritance in an app. I have an Entity class with a property name. This class is inherited by two other classes: Store and Person. The Entity model has a one-to-many relationship with a Transaction class. I can list all my Entity models in a List with a @Query annotation without a problem. However, then I try to access the name property of an Entity from a Transaction relationship, the app crashes with the following error: Thread 1: Fatal error: Never access a full future backing data - PersistentIdentifier(id: SwiftData.PersistentIdentifier.ID(backing: SwiftData.PersistentIdentifier.PersistentIdentifierBacking.managedObjectID(0x96530ce28d41eb63 <x-coredata://DABFF7BB-C412-474E-AD50-A1F30AC6DBE9/Person/p4>))) with Optional(F07E7E23-F8F0-4CC0-B282-270B5EDDC7F3) From my attempts to fix the issue, I noticed that: The crash seems related to the relationships with classes that has inherit from another class, since it only happens there. When I create new data, I can usually access it without any problem. The crash mostly happens after reloading the app. This error has been mentioned on the forum (for example here), but in a context not related with inheritance. You can find the full code here. For reference, my models looks like this: @Model class Transaction { @Attribute(.unique) var id: String var name: String var date: Date var amount: Double var entity: Entity? var store: Store? { entity as? Store } var person: Person? { entity as? Person } init( id: String = UUID().uuidString, name: String, amount: Double, date: Date = .now, entity: Entity? = nil, ) { self.id = id self.name = name self.amount = amount self.date = date self.entity = entity } } @Model class Entity: Identifiable { @Attribute(.preserveValueOnDeletion) var name: String var lastUsedAt: Date @Relationship(deleteRule: .cascade, inverse: \Transaction.entity) var operations: [Transaction] init( name: String, lastUsedAt: Date = .now, operations: [Transaction] = [], ) { self.name = name self.lastUsedAt = lastUsedAt self.operations = operations } } @available(iOS 26, *) @Model class Store: Entity { @Attribute(.unique) var id: String var locations: [Location] init( id: String = UUID().uuidString, name: String, lastUsedAt: Date = .now, locations: [Location] = [], operations: [Transaction] = [] ) { self.locations = locations self.id = id super.init(name: name, lastUsedAt: lastUsedAt, operations: operations) } } In order to reproduce the error: Run the app in the simulator. Click the + button to create a new transaction. Relaunch the app, then click on any transaction. The app crashes when it tries to read te name property while building the details view.

Hello, I'm planning to had an onboarding to one of my apps. I am thinking about a way for a user to not see the onboarding again if he installs the app on another device. So for example, the user completes the onboarding on its iPhone, then downloads the app on its iPad and launch it, he doesn't see the onboarding a second time. I thought about using iCloud NSUbiquitousKeyValueStored to store the onboarding completion state. But I'm not sure when the data is synced to the other device logged into the same Apple account: Immediately even if the app is not installed on the other device (independent from the app, only iCloud thing)? At the same time as the app install on the other device? After the app is first launched on the other device? Of course synchronisation will depend on the Internet connection, speed, etc. so the app should handle the case where the data is not here but what would be the best case scenario? Thank you, Axel

Hi, I'm implementing iCloud backup functionality in my web application using CloudKit JS, but I'm running into some issues. I'd appreciate any help you can provide. Issue: The iCloud backup feature isn't working properly in our web app. I believe I've correctly set up the Apple Developer Program registration and API token generation. While a demo implementation works perfectly with iCloud backup, our app implementation is failing. Specifically: "Sign in with Apple" succeeds However, ck.getDefaultContainer().setupAuth() returns null In the working demo, setupAuth() returns a proper value Even after logging in through the redirect URL provided in the "421 Misdirected Request" error response and executing setupAuth(), it still returns null I've essentially copied the working demo code directly, so I suspect the issue might be related to token generation, permissions, or account configuration. Questions: Could you provide detailed step-by-step instructions for implementing iCloud backup in a web application? I've noticed there are configuration items in the Developer Console and Certificates console, so I may have missed something in one of these areas. Based on the symptoms described, what are the possible causes for setupAuth() returning null in CloudKit JS? Could configuration issues be indirectly causing this, or is it more likely a timing issue or SDK coding problem? Specifically regarding the 421 error and redirect flow - is there something in the configuration that could cause setupAuth() to return null even after successful authentication through the redirect? Thanks in advance for your help!

One question I often see on DevForums and in my day DTS job is if a Core Data object managed by NSPersistentCloudKitContainer can be shared with other iCloud users. The answer is yes but you need to do it using CloudKit API directly because NSPersistentCloudKitContainer doesn’t support CloudKit shared database (CKContainer.sharedCloudDatabase) today. Assuming you have a Core Data object, let’s say a document, that you’d like to collaborate with your colleagues: You are the document owner and can use NSPersistentCloudKitContainer to fully manages the document and synchronize it across your devices. You can grab a CloudKit record associated with your document from NSPersistentCloudKitContainer using record(for:) or recordID(for:), and share it to your colleagues using UICloudSharingController. See our Sharing CloudKit Data with Other iCloud Users - https://developer.apple.com/documentation/cloudkit/sharing_cloudkit_data_with_other_icloud_users sample for how to share a CloudKit record. After accepting the sharing, your colleague, as a participant, can view or edit the shared document. The document resides in the participant’s CloudKit shared database and you have to manage it with your own code. When your colleague edits and saves the shared document, the changes go to the owner’s private database, and eventually synchronize to NSPersistentCloudKitContainer on the owner side.  As you can see, you need to implement #2 and #3 with your own code because NSPersistentCloudKitContainer can’t manage the data in the participant's shared database. If you have any difficulty after going through the above sample code, you can contact Apple’s DTS for help.

We are trying to solve for the following condition with SwiftData + CloudKit: Lots of data in CloudKit Perform "app-reset" to clear data & App settings and start fresh. Reset data models with try modelContext.delete(model:_) myModel.count() confirms local deletion (0 records); but iCloud Console shows expectedly slow process to delete. Old CloudKit data is returning during the On Boarding process. Questions: • Would making a new iCloud Zone for each reset work around this, as the new zone would be empty? We're having trouble finding details about how to do this with SwiftData. • Would CKSyncEngine have a benefit over the default SwiftData methods? Open to hearing if anyone has experienced a similar challenge and how you worked around it!

I'm using Swift Data for an app that requires iOS 18. All of my models conform to a protocol that guarantees they have a 'serverID' String variable. I wrote a function that would allow me to pass in a serverID String and have it fetch the model object that matched. Because I am lazy and don't like writing the same functions over and over, I used a Self reference so that all of my conforming models get this static function. Imagine my model is called "WhatsNew". Here's some code defining the protocol and the fetching function. protocol RemotelyFetchable: PersistentModel { var serverID: String { get } } extension WhatsNew: RemotelyFetchable {} extension RemotelyFetchable { static func fetchOne(withServerID identifier: String, inContext modelContext: ModelContext) -> Self? { var fetchDescriptor = FetchDescriptor<Self>() fetchDescriptor.predicate = #Predicate<Self> { $0.serverID == identifier } do { let allModels = try modelContext.fetch(fetchDescriptor) return allModels.first } catch { return nil } } } Worked great! Or so I thought... I built this and happily ran a debug build in the Simulator and on devices for months while developing the initial version but when I went to go do a release build for TestFlight, that build reliably crashed on every device with a message like this: SwiftData/DataUtilities.swift:65: Fatal error: Couldn't find \WhatsNew. on WhatsNew with fields [SwiftData.Schema.PropertyMetadata(name: "serverID", keypath: \WhatsNew., defaultValue: nil, metadata: Optional(Attribute - name: , options: [unique], valueType: Any, defaultValue: nil, hashModifier: nil)), SwiftData.Schema.PropertyMetadata(name: "title", keypath: \WhatsNew., defaultValue: nil, metadata: nil), SwiftData.Schema.PropertyMetadata(name: "bulletPoints", keypath: \WhatsNew.)>, defaultValue: nil, metadata: nil), SwiftData.Schema.PropertyMetadata(name: "dateDescription", keypath: \WhatsNew., defaultValue: nil, metadata: nil), SwiftData.Schema.PropertyMetadata(name: "readAt", keypath: \WhatsNew.)>, defaultValue: nil, metadata: nil)] It seems (cannot confirm) that something in the release build optimization process is stripping out some metadata / something about these models that makes this predicate crash. Tested on iOS 18.0 and 18.1 beta. How can I resolve this? I have two dozen types that conform to this protocol. I could manually specialize this function for every type myself but... ugh.

Hey all, This is my first app with Swift, and first app using CloudKit / iCloud - although I have launched other iOS app successfully. When I created the app, I selected "none" for storage my bundle identifier looks like this: io.mysite.appname I have the iCloud capability added, with CloudKit checked, and the container also checked that looks like this: iCloud.io.mysite.appname Push Notificaitons capability is also added, but there is no configuration. I have tried automatically managed signing, as well as a manually created provisioning profile.. Every time I build the app onto my device - when I check it out in settings, icloud is not listed. When I go through iCloud into icloud drive, the app is also not listed. I have cleaned the build many times, deleted and reinstalled the app on my phone many times. I am definitely logged into iCloud etc. Obviously I have spent plenty of times trying to debug with various LLMs, but we all seem to be at a loss for what I'm missing or doing wrong. Would love any tips or pointers I may be missing, thank you!

I am trying to add a custom JSON DataStore and DataStoreConfiguration for SwiftData. Apple kindly provided some sample code in the WWDC24 session, "Create a custom data store with SwiftData", and (once updated for API changes since WWDC) that works fine. However, when I try to add a relationship between two classes, it fails. Has anyone successfully made a JSONDataStore with a relationship? Here's my code; firstly the cleaned up code from the WWDC session: import SwiftData final class JSONStoreConfiguration: DataStoreConfiguration { typealias Store = JSONStore var name: String var schema: Schema? var fileURL: URL init(name: String, schema: Schema? = nil, fileURL: URL) { self.name = name self.schema = schema self.fileURL = fileURL } static func == (lhs: JSONStoreConfiguration, rhs: JSONStoreConfiguration) -> Bool { return lhs.name == rhs.name } func hash(into hasher: inout Hasher) { hasher.combine(name) } } final class JSONStore: DataStore { typealias Configuration = JSONStoreConfiguration typealias Snapshot = DefaultSnapshot var configuration: JSONStoreConfiguration var name: String var schema: Schema var identifier: String init(_ configuration: JSONStoreConfiguration, migrationPlan: (any SchemaMigrationPlan.Type)?) throws { self.configuration = configuration self.name = configuration.name self.schema = configuration.schema! self.identifier = configuration.fileURL.lastPathComponent } func save(_ request: DataStoreSaveChangesRequest<DefaultSnapshot>) throws -> DataStoreSaveChangesResult<DefaultSnapshot> { var remappedIdentifiers = [PersistentIdentifier: PersistentIdentifier]() var serializedData = try read() for snapshot in request.inserted { let permanentIdentifier = try PersistentIdentifier.identifier(for: identifier, entityName: snapshot.persistentIdentifier.entityName, primaryKey: UUID()) let permanentSnapshot = snapshot.copy(persistentIdentifier: permanentIdentifier) serializedData[permanentIdentifier] = permanentSnapshot remappedIdentifiers[snapshot.persistentIdentifier] = permanentIdentifier } for snapshot in request.updated { serializedData[snapshot.persistentIdentifier] = snapshot } for snapshot in request.deleted { serializedData[snapshot.persistentIdentifier] = nil } try write(serializedData) return DataStoreSaveChangesResult<DefaultSnapshot>(for: self.identifier, remappedIdentifiers: remappedIdentifiers) } func fetch<T>(_ request: DataStoreFetchRequest<T>) throws -> DataStoreFetchResult<T, DefaultSnapshot> where T : PersistentModel { if request.descriptor.predicate != nil { throw DataStoreError.preferInMemoryFilter } else if request.descriptor.sortBy.count > 0 { throw DataStoreError.preferInMemorySort } let objs = try read() let snapshots = objs.values.map({ $0 }) return DataStoreFetchResult(descriptor: request.descriptor, fetchedSnapshots: snapshots, relatedSnapshots: objs) } func read() throws -> [PersistentIdentifier : DefaultSnapshot] { if FileManager.default.fileExists(atPath: configuration.fileURL.path(percentEncoded: false)) { let decoder = JSONDecoder() decoder.dateDecodingStrategy = .iso8601 let data = try decoder.decode([DefaultSnapshot].self, from: try Data(contentsOf: configuration.fileURL)) var result = [PersistentIdentifier: DefaultSnapshot]() data.forEach { s in result[s.persistentIdentifier] = s } return result } else { return [:] } } func write(_ data: [PersistentIdentifier : DefaultSnapshot]) throws { let encoder = JSONEncoder() encoder.dateEncodingStrategy = .iso8601 encoder.outputFormatting = [.prettyPrinted, .sortedKeys] let jsonData = try encoder.encode(data.values.map({ $0 })) try jsonData.write(to: configuration.fileURL) } } The data model classes: import SwiftData @Model class Settings { private(set) var version = 1 @Relationship(deleteRule: .cascade) var hack: Hack? = Hack() init() { } } @Model class Hack { var foo = "Foo" var bar = 42 init() { } } Container: lazy var mainContainer: ModelContainer = { do { let url = // URL to file let configuration = JSONStoreConfiguration(name: "Settings", schema: Schema([Settings.self, Hack.self]), fileURL: url) return try ModelContainer(for: Settings.self, Hack.self, configurations: configuration) } catch { fatalError("Container error: \(error.localizedDescription)") } }() Load function, that saves a new Settings JSON file if there isn't an existing one: @MainActor func loadSettings() { let mainContext = mainContainer.mainContext let descriptor = FetchDescriptor<Settings>() let settingsArray = try? mainContext.fetch(descriptor) print("\(settingsArray?.count ?? 0) settings found") if let settingsArray, let settings = settingsArray.last { print("Loaded") } else { let settings = Settings() mainContext.insert(settings) do { try mainContext.save() } catch { print("Error saving settings: \(error)") } } } The save operation creates a JSON file, which while it isn't a format I would choose, is acceptable, though I notice that the "hack" property (the relationship) doesn't have the correct identifier. When I run the app again to load the data, I get an error (that there wasn't room to include in this post). Even if I change Apple's code to not assign a new identifier, so the relationship property and its pointee have the same identifier, it still doesn't load. Am I doing something obviously wrong, or are relationships not supported in custom data stores?