In Xcode 15.0.1, I created a new project to start working with SwiftData. I did this by creating a default App project and checking the Use SwiftData checkbox. The resulting project contains just three files: an app entry point file, a ContentView SwiftUI view file, and an Item model file. The only change I made was to annotate the default Item timestamp property with a .transformable attribute. Here is the resulting model: @Model final class Item { @Attribute(.transformable(by: TestVT.self)) var timestamp: Date // Only updated this line init(timestamp: Date) { self.timestamp = timestamp } } And here is the definition of TestVT. It is a basic ValueTransformer that simply tries to store the Date as a NSNumber: // Added this class TestVT: ValueTransformer { static let name = NSValueTransformerName("TestVT") override class func transformedValueClass() -> AnyClass { NSNumber.self } override class func allowsReverseTransformation() -> Bool { true } override func transformedValue(_ value: Any?) -> Any? { guard let date = value as? Date else { return nil } let ti = date.timeIntervalSince1970 return NSNumber(value: ti) } override func reverseTransformedValue(_ value: Any?) -> Any? { guard let num = value as? NSNumber else { return nil } let ti = num.doubleValue as TimeInterval return Date(timeIntervalSince1970: ti) } } And finally, I made sure to register my ValueTransformer but updating the sharedModelContainer definition in the App: var sharedModelContainer: ModelContainer = { ValueTransformer.setValueTransformer(TestVT(), forName: TestVT.name) // Only added this line let schema = Schema([ Item.self, ]) let modelConfiguration = ModelConfiguration(schema: schema, isStoredInMemoryOnly: false) do { return try ModelContainer(for: schema, configurations: [modelConfiguration]) } catch { fatalError("Could not create ModelContainer: \(error)") } }() Prior to Xcode 15.1, this was working fine. However, now when I try to create an item when running the app I get the following error: Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Unacceptable type of value for attribute: property = "timestamp"; desired type = NSNumber; given type = __NSTaggedDate; value = 2023-12-14 01:47:11 +0000.' I'm unsure of why this stopped working. The error seems to be complaining about the input being of type Date when NSNumber was expected, but I thought that's what the ValueTransformer was supposed to be doing. Important note: prior to Xcode 15.1, I did not originally override the transformedValueClass() and everything was working but in the new Xcode when launching the app I was getting a Thread 1: EXC_BAD_ACCESS (code=1, address=0x0) on the return try ModelContainer(...) line. Removing the .transformable property from my model fixed the issue. That's why I added the override here, because I think the docs indicate overriding it as well and I missed that the first time. This being said, I think the code I have is what a correct ValueTransformer would look like. If anyone has experienced this issue, or has a working ValueTransformer for SwiftData in Xcode 15.1, please let me know. Appreciate any help with this issue. Thanks so much!

When I logged into my cloudkit console to inspect the database for some debugging work I couldn't access the private database. It keeps saying "failed to access iCloud data, please signi n again". No matter how many times I sign in again, whether with password or passwordless key it keeps saying the same thing. It says that message when I click on Public database, and private and shared databases are below it. I only noticed this a couple of days ago. It's done this in the past, but I eventually got back into the database but I don't know what changed to make it work.

My app has been in the App Store a few months. In that time I've added a few updates to my SwiftData schema using a MigrationPlan, and things were seemingly going ok. But then I decided to add CloudKit syncing. I needed to modify my models to be compatible. So, I added another migration stage for it, changed the properties as needed (making things optional or adding default values, etc.). In my tests, everything seemed to work smoothly updating from the previous version to the new version with CloudKit. So I released it to my users. But, that's when I started to see the crashes and error reports come in. I think I've narrowed it down to when users update from older versions of the app. I was finally able to reproduce this on my end, and Core Data is throwing an error when loading the ModelContainer saying "CloudKit integration requires that all attributes be optional, or have a default value set." Even though I did this in the latest schema. It’s like it’s trying to load CloudKit before performing the schema migration, and since it can’t, it just fails and won’t load anything. I’m kinda at a loss how to recover from this for these users other than tell them to delete their app and restart, but obviously they’ll lose their data that way. The only other idea I have is to setup some older builds on TestFlight and direct them to update to those first, then update to the newest production version and hope that solves it. Any other ideas? And what can I do to prevent this for future users who maybe reinstall the app from an older version too? There's nothing special about my code for loading the ModelContainer. Just a basic: let container = try ModelContainer( for: Foo.self, Bar.self, migrationPlan: SchemaMigration.self, configurations: ModelConfiguration(cloudKitDatabase: .automatic) )

I'm sorta baffled right now. I am trying to wonder how I might detect a updated SQL Store in an older app. have a baseline app, and create a SQL-based repository in an updated app, change the model and verify that you can see the updated model version. Using lightweight migration re-run the older app (which will inherit the newer SQL repository). YIKES - no error when creating the NSPersistenStoreCoordinator! Nothing in the metadata to imply the store is newer than the model: [_persistentStoreCoordinator metadataForPersistentStore:store] My question: is there any way to detect this condition? David

I'm having some trouble with the following function from the CKSyncEngineDelegate protocol. func nextRecordZoneChangeBatch(_ context: CKSyncEngine.SendChangesContext, syncEngine: CKSyncEngine) async -> CKSyncEngine.RecordZoneChangeBatch? { The sample code from the documentation is func nextRecordZoneChangeBatch( _ context: CKSyncEngine.SendChangesContext, syncEngine: CKSyncEngine ) async -> CKSyncEngine.RecordZoneChangeBatch? { // Get the pending record changes and filter by the context's scope. let pendingChanges = syncEngine.state.pendingRecordZoneChanges .filter { context.options.zoneIDs.contains($0) } // Return a change batch that contains the corresponding materialized records. return await CKSyncEngine.RecordZoneChangeBatch( pendingChanges: pendingChanges) { self.recordFor(id: $0) } } init?(pendingChanges: [CKSyncEngine.PendingRecordZoneChange], recordProvider: (CKRecord.ID) -> (CKRecord?)) works fine for the sample app which only has one record type, but it seems incredible inefficient for my app which has a dozen different record types. The recordProvider gives you a CKRecord.ID, but not the CKRecord.RecordType. Searching each record type for a matching ID seems very inefficient. Doesn't the CKSyncEngine.PendingRecordZoneChange contain an array of CKRecords, not just CKRecord.IDs? According to the documentation CKSyncEngine.RecordZoneChangeBatch has a recordsToSave property, but Xcode reports 'CKSyncEngine.PendingRecordZoneChange' has no member 'recordsToSave' I'm looking for someway to get the CKRecords from syncEngine.state.pendingRecordZoneChanges.

In my recent endeavor, I aimed to introduce new Fetch Index Elements to the Core Data model of my iOS application. To achieve this, I followed a process of lightweight migration, detailed as follows: Navigate to Editor > Add Model Version to create a new version of the data model. Name the new version with a sequential identifier (e.g., MyAppModelV3.xcdatamodel) based on the naming convention of previous models. Select the newly created version, MyAppModelV3.xcdatamodel, as the active model. Mark this new version as the "Current" model in the Xcode properties panel on the right. In the new version of the model, MyAppModelV3.xcdatamodel, and add the new Fetch Index Elements there. Also, insert "v3" in the Versioning Hash Modifier field of affected entity, to indicate this modification. Upon reflection, I realized that creating a new version of the xcdatamodel might not have been necessary for this particular case. However, it appears to have caused no adverse effects on the application's functionality. During testing, I executed the application in a simulated environment, initially running an older version of the app to inspect the database content with SQLite DB Browser. I then upgraded to the latest app version to verify that the migration was successfully completed without causing any crashes. Throughout this testing phase, I employed the -com.apple.CoreData.MigrationDebug 1 flag to monitor all SQL operations, ensuring that indexes were appropriately dropped and recreated for the affected entity. Following thorough testing, I deployed the update to production. The majority of users were able to upgrade to the new app version seamlessly. However, a small fraction reported crashes at startup, indicated by the following error message: Fatal error: Unresolved error Error Domain=NSCocoaErrorDomain Code=134110 "An error occurred during persistent store migration." UserInfo={NSUnderlyingError=0x2820ad3e0 {Error Domain=NSCocoaErrorDomain Code=134100 "The managed object model version used to open the persistent store is incompatible with the one that was used to create the persistent store." UserInfo={metadata={ NSPersistenceFrameworkVersion = 1338; NSStoreModelVersionChecksumKey = "qcPf6+DfpsPrDQ3j1EVXcBIrFe1O0R6IKd30sJf4IrI="; NSStoreModelVersionHashes = { NSAttachment = {length = 32, ... Strangely, the only way I could replicate this issue in the simulator was by running the latest version of the app followed by reverting to an older version, a scenario unlikely to occur in a real-world setting. This raises the question: How could this situation arise with actual users, considering they would typically move from an old to a new version rather than the reverse? I am reaching out to the community for insights or advice on this matter. Has anyone else encountered a similar problem during the Core Data migration process? How did you resolve it?

According to my experiments SwiftData does not work with model attributes of primitive type UInt64. More precisely, it crashes in the getter of a UInt64 attribute invoked on an object fetched from the data store. With Core Data persistent UInt64 attributes are not a problem. Does anyone know whether SwiftData will ever support UInt64?

I have an Apple app that uses SwiftData and icloud to sync the App's data across users' devices. Everything is working well. However, I am facing the following issue: SwiftData does not support public sharing of the object graph with other users via iCloud. How can I overcome this limitation without stopping using SwiftData? Thanks in advance!

We worked with SwiftData, and once CloudKit was integrated, the synchronization worked well. Even if I rerun the app, it works just as well. However, when I delete the app and reinstall it, I get a Token Expired error and CloudKit doesn't work properly. My code is organized like this public lazy var modelContext: ModelContext = { ModelContext(modelContainer) }() private lazy var modelContainer: ModelContainer = { let schema = Schema([ Entity1.self, Entity2.self, Entity3.self, ]) let modelConfiguration = ModelConfiguration( schema: schema, groupContainer: .identifier("myGroupContainer"), cloudKitDatabase: .automatic ) do { return try ModelContainer(for: schema, configurations: [modelConfiguration]) } catch { fatalError("Could not create ModelContainer: \(error)") } }() The error content is as follows error: CoreData+CloudKit: -[PFCloudKitImportRecordsWorkItem fetchOperationFinishedWithError:completion:]_block_invoke(707): <PFCloudKitImporterZoneChangedWorkItem: 0x3022c0000 - <NSCloudKitMirroringImportRequest: 0x3036e7ac0> 1A7E53D4-E95B-423F-8887-66360F6D8865> { ( "<CKRecordZoneID: 0x301bb1bf0; zoneName=com.apple.coredata.cloudkit.zone, ownerName=__defaultOwner__>" ) } - Fetch finished with error: <CKError 0x301bb5650: "Partial Failure" (2/1011); "Couldn't fetch some items when fetching changes"; uuid = 3F346302-C3EE-4F72-820C-988287C92C0A; container ID = "MyContainerID"; partial errors: { com.apple.coredata.cloudkit.zone:__defaultOwner__ = <CKError 0x301bb1830: "Change Token Expired" (21/2026); server message = "client knowledge differs from server knowledge"; op = 515034AC3ADC4348; uuid = 3F346302-C3EE-4F72-820C-988287C92C0A> }> error: CoreData+CloudKit: -[NSCloudKitMirroringDelegate _importFinishedWithResult:importer:](1390): <PFCloudKitImporter: 0x3000a1240>: Import failed with error: <CKError 0x301bb5650: "Partial Failure" (2/1011); "Couldn't fetch some items when fetching changes"; uuid = 3F346302-C3EE-4F72-820C-988287C92C0A; container ID = "MyContainerID"; partial errors: { com.apple.coredata.cloudkit.zone:__defaultOwner__ = <CKError 0x301bb1830: "Change Token Expired" (21/2026); server message = "client knowledge differs from server knowledge"; op = 515034AC3ADC4348; uuid = 3F346302-C3EE-4F72-820C-988287C92C0A> }> Forcing the ModelContainer to be reinitialized fixes the problem, it's a problem to get this error in the first place, the error doesn't even go to fatal for me, so I don't even know how to verify that it's happening. Is there something I'm doing wrong, or do you have any good ideas for solving the same problem?

Hello, I’m upgrading my app from Core Data to SwiftData. Due to my old setup the Core Data store has an explicitly name like „Something.sqlite“, because it was defined via NSPersistentContainer(name: "Something") before switching to SwiftData. Now my goal is to migrate the Core Data stack to SwiftData, while moving it to an App Group (for Widget support) as well as enable iCloud sync via CloudKit. Working Migration without App Group & CloudKit I’ve managed to get my migration running without migrating it to an App Group and CloudKit support like so: @main struct MyAppName: App { let container: ModelContainer init() { // Legacy placement of the Core Data file. let dataUrl = URL.applicationSupportDirectory.appending(path: "Something.sqlite") do { // Create SwiftData container with migration and custom URL pointing to legacy Core Data file container = try ModelContainer( for: Foo.self, Bar.self, migrationPlan: MigrationPlan.self, configurations: ModelConfiguration(url: dataUrl)) } catch { fatalError("Failed to initialize model container.") } } var body: some Scene { WindowGroup { ContentView() } .modelContainer(container) } } How To Migrate to App Group & CloudKit? I’ve already tried to use the ModelConfiguration with a name, but it seems to only look for a .store file and thus doesn’t copy over the Core Data contents. let fullSchema = Schema([Foo.self, Bar.self]) let configuration = ModelConfiguration("Something", schema: fullSchema) Can someone help me how to do this migration or point me into the right direction? I can’t find anything relating this kind of migration …

I'm currently using Xcode 16 Beta (16A5171c) and I'm getting a crash whenever I attempt to fetch using my ModelContext in my SwiftUI video using the environment I'm getting a crash specifically on iOS 18 simulators. I've opened up a feedback FB13831520 but it's worth noting that I can run the code I'll explain in detail below on iOS 17+ simulator and devices just fine. I'm getting the following crash: *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'The specified URI is not a valid Core Data URI: x-coredata:///MyApp/XXXXX-XXXXX-XXXX-XXXX-XXXXXXXXXXXX' It's almost as if on iOS18 SwiftData is unable to find the file on the simulator to perform CRUD operations. All I'm doing in my project is simply fetching data using the modelContext. func contains(_ model: MyModel, in context: ModelContext) -> Bool { let objId = palette.persistentModelID let fetchDesc = FetchDescriptor<MyModel>(predicate: #Predicate { $0.persistentModelID == objId }) let itemCount = try? context.fetchCount(fetchDesc) return itemCount != 0 }

I've just tried to update a project that uses SwiftData to Swift 6 using Xcode 16 beta 1, and it's not working due to missing Sendable conformance on a couple of types (MigrationStage and Schema.Version): struct LocationsMigrationPlan: SchemaMigrationPlan { static let schemas: [VersionedSchema.Type] = [LocationsVersionedSchema.self] static let stages: [MigrationStage] = [] } struct LocationsVersionedSchema: VersionedSchema { static let models: [any PersistentModel.Type] = [ Location.self ] static let versionIdentifier = Schema.Version(1, 0, 0) } This code results in the following errors: error: static property 'stages' is not concurrency-safe because non-'Sendable' type '[MigrationStage]' may have shared mutable state static let stages: [MigrationStage] = [] ^ error: static property 'versionIdentifier' is not concurrency-safe because non-'Sendable' type 'Schema.Version' may have shared mutable state static let versionIdentifier = Schema.Version(1, 0, 0) ^ Am I missing something, or is this a bug in the current seed? I've filed this as FB13862584.

When trying to run my document-based iPad app using iPadOS 18 beta and Xcode 16 beta, I get an error like the following after opening a document: Thread 1: Fatal error: Failed to identify a store that can hold instances of SwiftData._KKMDBackingData<MyProject.MyModel> from [:] In order to help track down what is going wrong, I downloaded the sample app from WWDC23 session "Build an app with SwiftData" found here: https://developer.apple.com/documentation/swiftui/building-a-document-based-app-using-swiftdata When I try to run the end-state of that sample code, I get a similar error when running the app on my iPad and creating a new deck: Thread 1: Fatal error: Failed to identify a store that can hold instances of SwiftData._KKMDBackingData<SwiftDataFlashCardSample.Card> from [:] Given that the sample project is generating the same error as my own project, is this a problem with SwiftData and document-based apps in general? Or is there a change of approach that I should try?

I have a document app built using SwiftData because frankly I'm too lazy to learn how to use FileDocument. The app's title is "Artsheets," and I'm using a document type that my app owns: com.wannafedor4.ArtsheetsDoc. The exported type identifier has these values: Description: Artsheets Document Identifier: com.wannafedor4.ArtsheetsDoc Conforms to: com.apple.package Reference URL: (none) Extensions: artsheets MIME Types: (none) And the code: ArtsheetsApp.swift import SwiftUI import SwiftData @main struct ArtsheetsApp: App { var body: some Scene { DocumentGroup(editing: Sheet.self, contentType: .package) { EditorView() } } } Document.swift import SwiftUI import SwiftData import UniformTypeIdentifiers @Model final class Sheet { var titleKey: String @Relationship(deleteRule: .cascade) var columns: [Column] init(titleKey: String, columns: [Column]) { self.titleKey = titleKey self.columns = columns } } @Model final class Column: Identifiable { var titlekey: String var text: [String] init(titlekey: String, text: [String]) { self.titlekey = titlekey self.text = text } } extension UTType { static var artsheetsDoc = UTType(exportedAs: "com.wannafedor4.artsheetsDoc") } I compiling for my iPhone 13 works, but then when creating a document I get this error: Failed to create document. Error: Error Domain=com.apple.DocumentManager Code=2 "No location available to save “Untitled”." UserInfo={NSLocalizedDescription=No location available to save “Untitled”., NSLocalizedRecoverySuggestion=Enable at least one location to be able to save documents.}

Since the iOS 18 and Xcode 16, I've been getting some really strange SwiftData errors when passing @Model classes around. The error I'm seeing is the following: SwiftData/BackingData.swift:409: Fatal error: This model instance was destroyed by calling ModelContext.reset and is no longer usable. PersistentIdentifier(id: SwiftData.PersistentIdentifier.ID(url: x-coredata://34EE9059-A7B5-4484-96A0-D10786AC9FB0/TestApp/p2), implementation: SwiftData.PersistentIdentifierImplementation) The same issue also happens when I try to retrieve a model from the ModelContext using its PersistentIdentifier and try to do anything with it. I have no idea what could be causing this. I'm guessing this is just a bug in the iOS 18 Beta, since I couldn't find a single discussion about this on Google, I figured I'd mention it. if someone has a workaround or something, that would be much appreciated.

I have encountered an issue that when using a ModelActor to sync data in the background, the app will crash if one of the operations is to remove a PersistentModel from the context. This is running on the latest beta of Xcode 16 with visionOS 1.2 as target and in Swift 6 language mode. The code is being executed in a ModelActor. The error is first thrown by: #5 0x00000001c3223280 in PersistentModel.getValue<τ_0_0>(forKey:) () Thread 1: Fatal error: Context is missing for Optional(SwiftData.PersistentIdentifier(id: SwiftData.PersistentIdentifier.ID(url: x-coredata://97AA86BC-475D-4509-9004-D1182ABA1922/Reminder/p303), implementation: SwiftData.PersistentIdentifierImplementation)) func globalSync() async { await fetchAndSyncFolders() let result = await fetchReminders() switch result { case .success(let ekReminders): var localReminders = (try? await fetch(FetchDescriptor<Reminder>())) ?? [] // Handle local reminders with nil ekReminderID by creating new EKReminders for them for reminder in localReminders { if reminder.ekReminderID == nil { await self.createEkReminder(reminder: reminder) } } // Re-fetch local reminders to include newly created EKReminderIDs localReminders = (try? await fetch(FetchDescriptor<Reminder>())) ?? [] var localReminderDict = [String: Reminder]() for reminder in localReminders { if let ekReminderID = reminder.ekReminderID { if let existingReminder = localReminderDict[ekReminderID] { self.delete(model: existingReminder) } else { localReminderDict[ekReminderID] = reminder } } } let ekReminderDict = createReminderLookup(byID: ekReminders) await self.syncReminders(localReminders: Array(localReminderDict.values), localReminderDict: localReminderDict, ekReminderDict: ekReminderDict) // Merge duplicates await self.mergeDuplicates(localReminders: localReminders) save() case .failure(let error): print("Failed to fetch reminders: \(error.localizedDescription)") } }

I have a background thread that is updating a swift data model Item using a ModelActor. The background thread runs processing an Item and updates the Item's status field. I notice that if I have a view like struct ItemListView: View { @Query private var items: [Items] var body: some View { VStack { ForEach(items) { item in ItemDetailView(item) } } } } struct ItemDetailView: View { var item: Item var body: some View { // expected: item.status automatically updates when the background thread updates the `Item`'s `status`. Text(item.status) // actual: This text never changes } } Then background updates to the Item's status in SwiftData does not reflect in the ItemDetailView. However, if I inline ItemDetailView in ItemListView like this: struct ItemListView: View { @Query private var items: [Items] var body: some View { VStack { ForEach(items) { item in // Put the contents of ItemDetailView directly in ItemListView Text(item.status) // result: item.status correctly updates when the background thread updates the item. } } } } Then the item's status text updates in the UI as expected. I suspect ItemDetailView does not properly update the UI because it just takes an Item as an input. ItemDetailView would need additional understanding of SwiftData, such as a ModelContext. Is there a way I can use ItemDetailView to show the Item's status and have the UI show the status as updated in the background thread? In case details about my background thread helps solve the problem, my thread is invoked from another view's controller like @Observable class ItemCreateController { func queueProcessingTask() { Task { let itemActor = ItemActor(modelContainer: modelContainer) await itemActor.setItem(item) await itemActor.process() } } } @ModelActor actor ItemActor { var item: Item? func setItem(_ item: Item) { self.item = modelContext.model(for: item.id) as? Item } func process() async { // task that runs processing on the Item and updates the Item's status as it goes. }

Hi, I am inserting two models where the "unique" attribute is the same. I was under the impression, that this should result in an upsert and not two inserts of the model, but that is not the case. See the test coding below for what I am doing (it is self contained, so if you want to try it out, just copy it into a test target). The last #expect statement fails because of the two inserts. Not sure if this is a bug (Xcode 16 beta 2 on Sonoma running an iOS 18 simulator) or if I am missing something here... // MARK: - UniqueItem - @Model final class UniqueItem { #Unique<UniqueItem>([\.no]) var timestamp = Date() var title: String var changed = false var no: Int init(title: String, no: Int) { self.title = title self.no = no } } // MARK: - InsertTests - @Suite("Insert Tests", .serialized) struct InsertTests { var sharedModelContainer: ModelContainer = { let schema = Schema([ UniqueItem.self, ]) let modelConfiguration = ModelConfiguration(schema: schema, isStoredInMemoryOnly: false) do { return try ModelContainer(for: schema, configurations: [modelConfiguration]) } catch { fatalError("Could not create ModelContainer: \(error)") } }() @Test("Test unique.") @MainActor func upsertAndModify() async throws { let ctx = sharedModelContainer.mainContext try ctx.delete(model: UniqueItem.self) let item = UniqueItem(title: "Item \(1)", no: 0) ctx.insert(item) let allFD = FetchDescriptor<UniqueItem>() let count = try ctx.fetchCount(allFD) #expect(count == 1) let updatedItem = UniqueItem(title: "Item \(1)", no: 0) updatedItem.changed = true ctx.insert(updatedItem) // we should still have only 1 item because of the unique constraint let allCount = try ctx.fetchCount(allFD) #expect(allCount == 1) } }

I am unsure the correct way to model my data. I have a swift data object and then some referenced objects. Is there ever a reason those should just be structs or should they always be swift data objects themselves? for example right now this is what I'm doing: @Model final class Exam { var timestamp: Date @Attribute(.unique) var examID: UUID var title: String var questions: [Question] ... } and Question is struct Question: Codable, Identifiable { var id: UUID var number: Int var points: Int var prompt: String var answer: String } is there any problem with this or should I not be using a Struct for Question and instead use another Swift Data object with @Relationship ? I thought since its a simple object just using a struct would be fine, however... when I create a new Question object, it seems to create SwiftUI retain cycles with the warning === AttributeGraph: cycle detected through attribute 633984 === in the terminal for example, Button("Add Question", systemImage: "questionmark.diamond") { let newQuestion = Question(id: UUID(), number: exam.questions.count+1, points: 1, prompt: "", answer: "", type: .multipleChoice) exam.questions.append(newQuestion) } So, is it ok to mix structs with swift data objects or is it not best practice? And is this causing the SwiftUI retain cycles or are the issues unrelated?

Starting point I have an app that is in production that has a single entity called CDShift. This is the class: @Model final class CDShift { var identifier: UUID = UUID() var date: Date = Date() ... } This is how this model is written in the current version. Where I need to go Now, I'm updating the app and I have to do some modifications, that are: add a new entity, called DayPlan add the relationship between DayPlan and CDShift What I did is this: enum SchemaV1: VersionedSchema { static var versionIdentifier = Schema.Version(1, 0, 0) static var models: [any PersistentModel.Type] { [CDShift.self] } @Model final class CDShift { var identifier: UUID = UUID() var date: Date = Date() } } To encapsulate the current CDShift in a version 1 of the schema. Then I created the version 2: enum SchemaV2: VersionedSchema { static var versionIdentifier = Schema.Version(2, 0, 0) static var models: [any PersistentModel.Type] { [CDShift.self, DayPlan.self] } @Model final class DayPlan { var identifier: UUID = UUID() var date: Date = Date() @Relationship(inverse: \CDShift.dayPlan) var shifts: [CDShift]? = [] } @Model final class CDShift { var identifier: UUID = UUID() var date: Date = Date() var dayPlan: DayPlan? = nil } } The migration plan Finally, I created the migration plan: enum MigrationPlan: SchemaMigrationPlan { static var schemas: [any VersionedSchema.Type] { [SchemaV1.self, SchemaV2.self] } static let migrateV1toV2 = MigrationStage.custom( fromVersion: SchemaV1.self, toVersion: SchemaV2.self) { context in // willMigrate, only access to old models } didMigrate: { context in // didMigrate, only access to new models let shifts = try context.fetch(FetchDescriptor<SchemaV2.CDShift>()) for shift in shifts { let dayPlan = DayPlan(date: shift.date) dayPlan.shifts?.append(shift) context.insert(dayPlan) } } static var stages: [MigrationStage] { print("MigrationPlan | stages called") return [migrateV1toV2] } } The ModelContainer Last, but not least, how the model container is created in the App: struct MyApp: App { private let container: ModelContainer init() { container = ModelContainer.appContainer } var body: some Scene { WindowGroup { ... } .modelContainer(container) } } This is the extension of ModelContainer: extension ModelContainer { static var appContainer: ModelContainer { let schema = Schema([ CDShift.self, DayPlan.self ]) let modelConfiguration = ModelConfiguration( schema: schema, isStoredInMemoryOnly: Ecosystem.current.isPreview, groupContainer: .identifier(Ecosystem.current.appGroupIdentifier) ) do { // let container = try ModelContainer(for: schema, configurations: modelConfiguration) let container = try ModelContainer(for: schema, migrationPlan: MigrationPlan.self, configurations: modelConfiguration) AMLogger.verbose("SwiftData path: \(modelConfiguration.url.path)") return container } catch (let error) { fatalError("Could not create ModelContainer: \(error)") } } } The error This has always worked perfectly until the migration. It crashes on the fatalError line, this is the error: Unable to find a configuration named 'default' in the specified managed object model. Notes It seems that the version of the store is never updated to 2, but it keeps staying on 1. I tried also using the lightweight migration, no crash, it seems it recognizes the new entity, but the store version is always 1. iCloud is enabled I thought that the context used in the custom migration blocks is not the "right" one that I use when I create my container If I use the lightweight migration, everything seems to work fine, but I have to manually do the association between the DayPlan and the CDShift objects Do you have an idea on how to help in this case?