Migrating existing app from NSPersistentContainer to NSPersistentCloudKitContainer - swift

Question

I have an app that uses local device only CoreData (NSPersistentContainer). I am looking to migrate so the app is compatible with NSPersistentCloudKitContainer. I understand all the CloudKit setup for NSPersistentCloudKitContainer, but how do I migrate the data that is on the player's phones to iCloud? (i.e. how do I migrate existing core data from NSPersistentContainer to NSPersistentCloudKitContainer)?

Answer 1

A good intro how to do this is given in the 2019 WWDC video „Using Core Data With CloudKit“.
The essential points are:
Replace NSPersistentContainer by ist subclass NSPersistentClouKitContainer.
Initialize the iCloud schema using the container function initializeCloudKitSchema (this has to be done only once after the core data model has been set up or changed).
In the iCloud Dashboard, make every custom type (these are the types starting with CD_) queryable.
In the iCloud Dashboard, set the security type of all CD_ record types for all authenticated users to read/write.
Implement history tracking for core data (here are Apple’s suggestions).
In case you have multiple persistent stores (e.g. a local store relevant only to one device, a private store shared with all users with the same Apple ID, and a shared store shared with other users), one way to set up this is the following:
private (set) lazy var persistentContainer: NSPersistentCloudKitContainer! = {
// This app uses 3 stores:
// - A local store that is user-specific,
// - a private store that is synchronized with the iCloud private database, and
// - a shared store that is synchronized with the iCloud shared database.
let persistentStoresLoadedLock = DispatchGroup.init() // Used to wait for loading the persistent stores
// Configure local store
// --------------------------------------------------------------------------------------------------
let appDocumentsDirectory = try! FileManager.default.url(for: .documentDirectory,
in: .userDomainMask,
appropriateFor: nil,
create: true)
let coreDataLocalURL = appDocumentsDirectory.appendingPathComponent("CoreDataLocal.sqlite")
let localStoreDescription = NSPersistentStoreDescription(url: coreDataLocalURL)
localStoreDescription.configuration = localConfigurationName
// --------------------------------------------------------------------------------------------------
// Create a container that can load the private store as well as CloudKit-backed stores.
let container = NSPersistentCloudKitContainer(name: appName)
assert(container.persistentStoreDescriptions.count == 1, "###\(#function): Failed to retrieve a persistent store description.")
let firstPersistentStoreDescription = container.persistentStoreDescriptions.first!
let storeURL = firstPersistentStoreDescription.url!
let storeURLwithoutLastPathComponent = storeURL.deletingLastPathComponent
// Configure private store
// --------------------------------------------------------------------------------------------------
let privateStoreDescription = firstPersistentStoreDescription
privateStoreDescription.configuration = privateConfigurationName
// The options below have to be set before loadPersistentStores
// Enable history tracking and remote notifications
privateStoreDescription.setOption(true as NSNumber, forKey: NSPersistentHistoryTrackingKey)
privateStoreDescription.setOption(true as NSNumber, forKey: NSPersistentStoreRemoteChangeNotificationPostOptionKey)
privateStoreDescription.cloudKitContainerOptions!.databaseScope = .private
// --------------------------------------------------------------------------------------------------
// Configure shared store
// --------------------------------------------------------------------------------------------------
let sharedStoreURL = storeURLwithoutLastPathComponent().appendingPathComponent("Shared")
let sharedStoreDescription = NSPersistentStoreDescription(url: sharedStoreURL)
sharedStoreDescription.configuration = sharedConfigurationName
sharedStoreDescription.timeout = firstPersistentStoreDescription.timeout
sharedStoreDescription.type = firstPersistentStoreDescription.type
sharedStoreDescription.isReadOnly = firstPersistentStoreDescription.isReadOnly
sharedStoreDescription.shouldAddStoreAsynchronously = firstPersistentStoreDescription.shouldAddStoreAsynchronously
sharedStoreDescription.shouldInferMappingModelAutomatically = firstPersistentStoreDescription.shouldInferMappingModelAutomatically
sharedStoreDescription.shouldMigrateStoreAutomatically = firstPersistentStoreDescription.shouldMigrateStoreAutomatically
// The options below have to be set before loadPersistentStores
// Enable history tracking and remote notifications
sharedStoreDescription.setOption(true as NSNumber, forKey: NSPersistentHistoryTrackingKey)
sharedStoreDescription.setOption(true as NSNumber, forKey: NSPersistentStoreRemoteChangeNotificationPostOptionKey)
sharedStoreDescription.cloudKitContainerOptions = NSPersistentCloudKitContainerOptions.init(containerIdentifier: "iCloud.com.zeh4soft.shop")
// For sharing see https://developer.apple.com/documentation/cloudkit/shared_records
// and https://medium.com/#adammillers/cksharing-step-by-step-33800c8950d2
sharedStoreDescription.cloudKitContainerOptions!.databaseScope = .shared
// --------------------------------------------------------------------------------------------------
container.persistentStoreDescriptions = [localStoreDescription, privateStoreDescription, sharedStoreDescription]
for _ in 1 ... container.persistentStoreDescriptions.count { persistentStoresLoadedLock.enter() }
container.loadPersistentStores(completionHandler: { (storeDescription, error) in
// The completion handler will be called once for each persistent store that is created.
guard error == nil else {
/*
Apple suggests to replace this implementation with code to handle the error appropriately.
However, there is not really an option to handle it, see <https://stackoverflow.com/a/45801384/1987726>.
Typical reasons for an error here include:
* The parent directory does not exist, cannot be created, or disallows writing.
* The persistent store is not accessible, due to permissions or data protection when the device is locked.
* The device is out of space.
* The store could not be migrated to the current model version.
Check the error message to determine what the actual problem was.
*/
fatalError("###\(#function): Failed to load persistent stores: \(error!)")
}
if storeDescription.configuration == self.privateConfigurationName {
/*
Only if the schema has been changed, it has to be re-initialized.
Due to an Apple bug, this can currently (iOS 13) only be done with a .private database!
A re-initialization requires to run the app once using the scheme with the "-initSchema" argument.
After schema init, ensure in the Dashboard:
For every custom type, recordID and modTime must have queryable indexes.
All CD record types must have read/write security type for authenticated users.
Run later always a scheme without the "-initSchema" argument.
*/
if ProcessInfo.processInfo.arguments.contains("-initSchema") {
do {
try container.initializeCloudKitSchema(options: .printSchema)
} catch {
print("-------------------- Could not initialize cloud kit schema --------------------")
}
}
}
persistentStoresLoadedLock.leave() // Called for all stores
})
let waitResult = persistentStoresLoadedLock.wait(timeout: .now() + 100) // Wait for local, private and shared stores loaded
if waitResult != .success { fatalError("Timeout while loading persistent stores") }
return container
} ()
EDIT:
privateConfigurationName, as well as sharedConfigurationName are Strings:
let privateConfigurationName = "Private"
let sharedConfigurationName = "Shared"
and Private and Shared are used as Configuration names in the Coredata model, e.g.:
One has to assign there the entities to the persistent store(s).
A warning:
I you assign the same entity to multiple persistent stores, a save of a managed context will store it in all assigned stores, except you assign a specific store, see this post.
Likewise, a fetch will fetch a record from all persistent stores the entity is assigned to, except you set affectedStores in the fetch request, see the docs.

Answer 2

I did the following :
Replaced NSPersistentContainer by NSPersistentCloudKitContainer
And added enabled history tracking
container = NSPersistentCloudKitContainer(name: "myApp") // <<<<< this
if inMemory {
container.persistentStoreDescriptions.first!.url = URL(fileURLWithPath: "/dev/null")
}
let description = container.persistentStoreDescriptions.first
description?.setOption(true as NSNumber,
forKey: NSPersistentHistoryTrackingKey) // <<<<< this
container.viewContext.automaticallyMergesChangesFromParent = true
container.loadPersistentStores(...)
EDIT: Well, I talked too quick. It does not work :(
I found that people have little tricks here https://developer.apple.com/forums/thread/120328
(for example edit the items to trigger a sync, or to manually transfer each object as said explained here https://medium.com/#dmitrydeplov/coredata-cloudkit-integration-for-a-live-app-57b6cfda84ad)
But there is no actual answers...