Sqd swiftdata sync

Syncing Model Data Across a Person's Devices (SwiftData)

Apple's guide for SwiftData automatic CloudKit synchronization.

SQLiteData context: SQLiteData replaces SwiftData but shares the same underlying CloudKit infrastructure. This skill is useful for understanding what SwiftData does automatically (so you know what SQLiteData's SyncEngine handles explicitly), and for migrating from SwiftData.

Required Capabilities

SwiftData requires two Xcode capabilities for iCloud sync:

1. iCloud capability — enable CloudKit, select/create a container
2. Background Modes capability — enable Remote notifications

See /skill sqd-cloudkit-setup for step-by-step setup.

CloudKit Schema Limitations

SwiftData macros generate schemas that may not be CloudKit-compatible:

SwiftData Macro	CloudKit Limitation
@Attribute(.unique)	CloudKit cannot enforce unique constraints (concurrent sync)
@Relationship	All relationships must be optional (CloudKit doesn't guarantee atomic processing). Set inverse explicitly if it can't be inferred. .deny delete rule not supported.

SQLiteData parallel: These same constraints apply — no UNIQUE constraints on synced tables, and foreign keys must use CASCADE/SET NULL/SET DEFAULT (not RESTRICT/NO ACTION).

Schema Initialization (Development Only)

SwiftData uses NSPersistentCloudKitContainer under the hood. To initialize the CloudKit schema during development:

#if DEBUG
try autoreleasepool {
    let desc = NSPersistentStoreDescription(url: config.url)
    let opts = NSPersistentCloudKitContainerOptions(
        containerIdentifier: "iCloud.com.example.Trips"
    )
    desc.cloudKitContainerOptions = opts
    desc.shouldAddStoreAsynchronously = false

    if let mom = NSManagedObjectModel.makeManagedObjectModel(for: [Trip.self, Accommodation.self]) {
        let container = NSPersistentCloudKitContainer(name: "Trips", managedObjectModel: mom)
        container.persistentStoreDescriptions = [desc]
        container.loadPersistentStores { _, err in
            if let err { fatalError(err.localizedDescription) }
        }
        try container.initializeCloudKitSchema()
        if let store = container.persistentStoreCoordinator.persistentStores.first {
            try container.persistentStoreCoordinator.remove(store)
        }
    }
}
#endif

SQLiteData doesn't need this — SyncEngine automatically creates CloudKit record types from your SQL schema.

Container Configuration

SwiftData auto-discovers the container from Entitlements.plist. To use a specific container:

let config = ModelConfiguration(cloudKitDatabase: .private("iCloud.com.example.Trips"))

To disable automatic sync (e.g., app already uses CloudKit directly):

let config = ModelConfiguration(cloudKitDatabase: .none)

Schemas Are Additive Only

Once deployed to production, you cannot:

• Delete model types
• Change existing model attributes

This matches SQLiteData's constraint: no removing/renaming columns or tables in deployed migrations.

Related Skills

• /skill sqd-cloudkit — SQLiteData's CloudKit sync (the replacement for SwiftData sync)
• /skill sqd-cloudkit-setup — Configuring iCloud capability and deploying schema to production