swiftdata

name swiftdata description Implement, review, or improve data persistence using SwiftData. Use when defining @Model classes with @Attribute, @Relationship, @Transient, #Unique, or #Index; when querying with @Query, #Predicate, FetchDescriptor, or SortDescriptor; when configuring ModelContainer and ModelContext for SwiftUI or background work with @ModelActor; when planning schema migrations with VersionedSchema and SchemaMigrationPlan; when setting up CloudKit sync with ModelConfiguration; or when coexisting with or migrating from Core Data. SwiftData Persist, query, and manage structured data in iOS 26+ apps using SwiftData with Swift 6.3. Contents Model Definition ModelContainer Setup CloudKit Sync CRUD Operations @Query in SwiftUI #Predicate FetchDescriptor Schema Versioning and Migration Core Data Coexistence Boundary Concurrency ( @ModelActor ) SwiftUI Integration Common Mistakes Review Checklist References Model Definition Apply @Model to a class (not struct). It synthesizes PersistentModel conformance. Model instances remain context/actor-bound; pass their PersistentIdentifier , not the instance, across actors. @Model class Trip { var name: String var destination: String var startDate: Date var endDate: Date var isFavorite: Bool = false @Attribute (.externalStorage) var imageData: Data ? @Relationship (deleteRule: .cascade, inverse: \ LivingAccommodation .trip) var accommodation: LivingAccommodation ? @Transient var isSelected: Bool = false // Always provide default init ( name : String , destination : String , startDate : Date , endDate : Date ) { self .name = name; self .destination = destination self .startDate = startDate; self .endDate = endDate } } @Attribute options : .externalStorage , .unique , .spotlight , .allowsCloudEncryption , .preserveValueOnDeletion , .ephemeral , .transformable(by:) . Rename: @Attribute(originalName: "old_name") . @Relationship : deleteRule: .cascade / .nullify (default)/ .deny / .noAction . Specify inverse: for reliable behavior. Unidirectional (iOS 18+): inverse: nil . #Unique (iOS 18+) : #Unique<Person>([\.firstName, \.lastName]) -- compound uniqueness. Inheritance (iOS 26+) : @Model class BusinessTrip: Trip { var company: String } . Supported types: Bool , Int / UInt variants, Float , Double , String , Date , Data , URL , UUID , Decimal , Array , Dictionary , Set , Codable enums, Codable structs and other compatible Codable value types, and relationships to @Model classes. ModelContainer Setup // Basic let container = try ModelContainer (for: Trip . self , LivingAccommodation . self ) // Configured let config = ModelConfiguration ( "Store" , isStoredInMemoryOnly: false , groupContainer: .identifier( "group.com.example.app" ), cloudKitDatabase: .private( "iCloud.com.example.app" )) let container = try ModelContainer (for: Trip . self , configurations: config) // With migration plan let container = try ModelContainer (for: SchemaV2 . Trip . self , migrationPlan: TripMigrationPlan . self ) // In-memory (previews/tests) let container = try ModelContainer (for: Trip . self , configurations: ModelConfiguration (isStoredInMemoryOnly: true )) CloudKit Sync ModelConfiguration(..., cloudKitDatabase:) opts a SwiftData store into automatic CloudKit sync, but app entitlements still gate sync. For any SwiftData CloudKit setup or schema-review task, include a separate Capabilities verdict before schema findings: Capabilities : Xcode target has the iCloud capability with CloudKit enabled and the intended container selected, plus Background Modes > Remote notifications. Without these entitlements, automatic sync is not fully configured even if cloudKitDatabase is set. Schema compatibility : no @Attribute(.unique) or #Unique ; relationships are optional, have explicit inverses where needed, and avoid .deny ; large Data uses @Attribute(.externalStorage) . Scalar attributes : do not make every scalar optional just for CloudKit. Keep required scalars nonoptional when initializers, defaults, or migrations provide valid values. Schema rollout : initialize the development schema only in nonproduction builds, verify it in CloudKit Dashboard, promote before release, and treat production changes as additive only. CRUD Operations For destructive batches and migrations, first run the exact predicate or version hop against a disposable copy and record affected identifiers/counts. Execute with explicit transaction/save semantics, refetch, and verify values, relationships, counts, and invariants. On failure, fix the predicate/schema and restore a pristine fixture before retrying; never blindly replay a destructive operation. // CREATE let trip = Trip (name: "Summer" , destination: "Paris" , startDate: .now, endDate: .now + 86400 * 7 ) modelContext.insert(trip) try modelContext.save() // or rely on autosave // READ let trips = try modelContext.fetch( FetchDescriptor < Trip >( predicate: # Predicate { $0 .destination == "Paris" }, sortBy: [ SortDescriptor (\.startDate)])) // UPDATE -- modify properties directly; autosave handles persistence trip.destination = "Rome" // DELETE modelContext.delete(trip) try modelContext.delete(model: Trip . self , where: # Predicate { $0 .isFavorite == false }) // TRANSACTION (atomic) try modelContext.transaction { modelContext.insert(trip); trip.isFavorite = true } @Query in SwiftUI struct TripListView : View { @Query (filter: # Predicate < Trip > { $0 .isFavorite == true }, sort: \.startDate, order: .reverse) private var favorites: [ Trip ] var body: some View { List (favorites) { trip in Text (trip.name) } } } // Dynamic query via init struct SearchView : View { @Query private var trips: [ Trip ] init ( search : String ) { _trips = Query (filter: # Predicate < Trip > { trip in search.isEmpty || trip.name.localizedStandardContains(search) }, sort: [ SortDescriptor (\.name)]) } var body: some View { List (trips) { trip in Text (trip.name) } } } // FetchDescriptor query struct RecentView : View { static var desc: FetchDescriptor < Trip > { var d = FetchDescriptor < Trip >(sortBy: [ SortDescriptor (\.startDate)]) d.fetchLimit = 5 ; return d } @Query ( RecentView .desc) private var recent: [ Trip ] var body: some View { List (recent) { trip in Text (trip.name) } } } #Predicate # Predicate < Trip > { $0 .destination.localizedStandardContains( "paris" ) } // String let now = Date () # Predicate < Trip > { $0 .startDate > now } // Date # Predicate < Trip > { $0 .isFavorite && $0 .destination != "Unknown" } // Compound # Predicate < Trip > { $0 .accommodation ? .name != nil } // Optional # Predicate < Trip > { $0 .tags.contains { $0 .name == "adventure" } } // Collection Supported: == , != , < , <= , > , >= , && , || , ! , contains() , allSatisfy() , filter() , starts(with:) , localizedStandardContains() , caseInsensitiveCompare() , arithmetic, conditional expressions, optional chaining and binding, nil coalescing, type casting. Avoid : loops, nested declarations, mutations, and arbitrary unsupported method calls. FetchDescriptor var d = FetchDescriptor < Trip >(predicate: ... , sortBy: [ ... ]) d.fetchLimit = 20 ; d.fetchOffset = 0 d.includePendingChanges = true d.propertiesToFetch = [\.name, \.startDate] d.relationshipKeyPathsForPrefetching = [\.accommodation] let trips = try modelContext.fetch(d) let count = try modelContext.fetchCount(d) let ids = try modelContext.fetchIdentifiers(d) try modelContext.enumerate(d, batchSize: 1000 ) { trip in trip.isProcessed = true } Schema Versioning and Migration enum SchemaV1 : VersionedSchema { static var versionIdentifier = Schema . Version ( 1 , 0 , 0 ) static var models: [ any PersistentModel . Type ] { [ Trip . self ] } @Model class Trip { var name: String ; init ( name : String ) { self .name = name } } } enum SchemaV2 : VersionedSchema { static var versionIdentifier = Schema . Version ( 2 , 0 , 0 ) static var models: [ any PersistentModel . Type ] { [ Trip . self ] } @Model class Trip { var name: String ; var startDate: Date ? // New property init ( name : String ) { self .name = name } } } enum TripMigrationPlan : SchemaMigrationPlan { static var schemas: [ any VersionedSchema . Type ] { [ SchemaV1 . self , SchemaV2 . self ] } static var stages: [ MigrationStage ] { [migrateV1toV2] } static let migrateV1toV2 = MigrationStage .lightweight( fromVersion: SchemaV1 . self , toVersion: SchemaV2 . self ) } // Custom migration for data transformation static let migrateV2toV3 = MigrationStage .custom( fromVersion: SchemaV2 . self , toVersion: SchemaV3 . self , willMigrate: nil , didMigrate: { context in let trips = try context.fetch( FetchDescriptor < SchemaV3 . Trip >()) for trip in trips { trip.displayName = trip.name.capitalized } try context.save() }) Lightweight handles: adding optional/defaulted properties, renaming ( originalName ), removing properties, adding model types. Verify the stage list covers every supported version hop, then migrate a fresh copy of each old store and assert post-migration data before release. Core Data Coexistence Boundary Use this skill when the work is to run SwiftData alongside an existing Core Data store or migrate screens from Core Data to SwiftData over time. Keep pure Core Data stack setup, NSManagedObjectContext , NSFetchRequest , and batch Core Data operations in the sibling core-data skill. For coexistence, give boundary guidance before detailed migration advice: Point SwiftData and Core Data at the same SQLite store URL. Match Core Data entity names, property names, types, and relationship shapes in the SwiftData @Model definitions. Use @Attribute(originalName:) for SwiftData properties whose persisted Core Data names differ from the Swift names. Do not write the same entity from both stacks at the same time; assign one stack as the writer for each entity during migration. Concurrency ( @ModelActor ) @ModelActor actor DataHandler { func importTrips ( _ records : [ TripRecord ]) throws { for r in records { modelContext.insert( Trip (name: r.name, destination: r.dest, startDate: r.start, endDate: r.end)) } try modelContext.save() // Always save explicitly in @ModelActor } func process ( tripID : PersistentIdentifier ) throws { guard let trip = self [tripID, as : Trip . self ] else { return } trip.isProcessed = true ; try modelContext.save() } } let handler = DataHandler (modelContainer: container) try await handler.importTrips(records) Rules : ModelContainer is Sendable . ModelContext is NOT -- use on its creating actor. Pass PersistentIdentifier (Sendable) across boundaries. Never pass @Model objects across actors. SwiftUI Integration @main struct MyApp : App { var body: some Scene { WindowGroup { ContentView () } .modelContainer(for: [ Trip . self , LivingAccommodation . self ]) } } struct DetailView : View { @Environment (\.modelContext) private var modelContext let trip: Trip var body: some View { Text (trip.name) Button ( "Delete" ) { modelContext.delete(trip) } } } # Preview { let config = ModelConfiguration (isStoredInMemoryOnly: true ) let container = try! ModelContainer (for: Trip . self , configurations: config) container.mainContext.insert( Trip (name: "Preview" , destination: "London" , startDate: .now, endDate: .now + 86400 )) return TripListView ().modelContainer(container) } Common Mistakes 1. @Model on struct -- Use class. @Model requires reference semantics. 2. @Transient without default -- Always provide default: @Transient var x: Bool = false . 3. Missing .modelContainer -- @Query returns empty without a container on the view hierarchy. 4. Passing model objects across actors: // WRONG: await handler.process(trip: trip) // CORRECT: await handler.process(tripID: trip.persistentModelID) 5. ModelContext on wrong actor: // WRONG: Task.detached { context.fetch(...) } // CORRECT: Use @ModelActor for background work 6. Unsupported #Predicate expressions: // WRONG: #Predicate<Trip> { $0.name.uppercased() == "PARIS" } // CORRECT: #Predicate<Trip> { $0.name.localizedStandardContains("paris") } 7. Flow control in #Predicate: // WRONG: #Predicate<Trip> { for tag in $0.tags { ... } } // CORRECT: #Predicate<Trip> { $0.tags.contains { $0.name == "x" } } 8. No save in @ModelActor -- Always call try modelContext.save() explicitly. 9. ObservableObject with @Model -- Never use ObservableObject / @Published . @Model generates Observable . Use @Query in views.