CloudCore

CloudCore is a framework that manages syncing between iCloud (CloudKit) and Core Data written on native Swift.

Features

• Leveraging NSPersistentHistory, local changes are pushed to CloudKit when online
• Pull manually or on CloudKit remote notifications.
• Differential sync, only changed object and values are uploaded and downloaded.
• Core Data relationships are preserved
• private database and shared database push and pull is supported.
• public database push is supported
• Parent-Child relationships can be defined for CloudKit Sharing
• Respects of Core Data options (cascade deletions, external storage).
• Knows and manages with CloudKit errors like userDeletedZone, zoneNotFound, changeTokenExpired, isMore.

How it works?

CloudCore is built using "black box" architecture, so it works invisibly for your application, you just need to add several lines to AppDelegate to enable it. Synchronization and error resolving is managed automatically.

1. CloudCore stores change tokens from CloudKit, so only changed data is downloaded.
2. When CloudCore is enabled (CloudCore.enable) it pulls changed data from CloudKit and subscribes to CloudKit push notifications about new changes.
3. When CloudCore.pull is called manually or by push notification, CloudCore pulls and saves changed data to Core Data.
4. When data is written to persistent container (parent context is saved) CloudCore founds locally changed data and pushed to CloudKit.
5. when leveraging NSPersistentHistory, changes are pushed only when online.

Installation

CocoaPods

CloudCore is available through CocoaPods. To install it, simply add the following line to your Podfile:

pod 'CloudCore', :git => 'https://github.com/deeje/CloudCore.git'

How to help?

Current version of framework hasn't been deeply tested and may contain errors. If you can test framework, I will be very glad. If you found an error, please post an issue.

Quick start

1. Enable CloudKit capability for you application:

2. For each entity type you want to sync, add this key: value pair to the UserInfo record of the entity:

• CloudCoreScopes: private

3. Also add 4 attributes to each entity:

• privateRecordData attribute with Binary type
• publicRecordData attribute with Binary type
• recordName attribute with String type
• ownerName attribute with String type

4. And enable 'Preserve After Deletion' for the following attributes

• privateRecordData
• publicRecordData

4. Make changes in your AppDelegate.swift file:

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
  // Register for push notifications about changes
  application.registerForRemoteNotifications()

  // Enable CloudCore syncing
  CloudCore.enable(persistentContainer: persistentContainer)

  return true
}

// Notification from CloudKit about changes in remote database
func application(_ application: UIApplication, didReceiveRemoteNotification userInfo: [AnyHashable : Any], fetchCompletionHandler completionHandler: @escaping (UIBackgroundFetchResult) -> Void) {
  // Check if it CloudKit's and CloudCore notification
  if CloudCore.isCloudCoreNotification(withUserInfo: userInfo) {
    // Fetch changed data from iCloud
    CloudCore.pull(using: userInfo, to: persistentContainer, error: nil, completion: { (fetchResult) in
      completionHandler(fetchResult.uiBackgroundFetchResult)
    })
  }
}

5. If you want to enable offline support, enable NSPersistentHistoryTracking when you initialize your Core Data stack

lazy var persistentContainer: NSPersistentContainer = {
	let container = NSPersistentContainer(name: "YourApp")

	let storeDescription = container.persistentStoreDescriptions.first
	storeDescription?.setOption(true as NSNumber, forKey: NSPersistentHistoryTrackingKey)

	container.loadPersistentStores { storeDescription, error in
		if let error = error as NSError? {
			// Replace this implementation with code to handle the error appropriately.                
		}
	}
	return container
}()

6. To identify changes from your app that should be pushed, save from a background ManagedObjectContexts named CloudCorePushContext

persistentContainer.performBackgroundTask { moc in
	moc.name = CloudCore.config.pushContextName
	// make changes to objects, properties, and relationships you want pushed via CloudCore
	try? context.save()
}

7. Make first run of your application in a development environment, fill an example data in Core Data and wait until sync completes. CloudKit will create needed schemas automatically.

Service attributes

CloudCore stores CloudKit information inside your managed objects, so you need to add attributes to your Core Data model for that. If required attributes are not found in an entity, that entity won't be synced.

Required attributes for each synced entity:

1. Private Record Data attribute with Binary type
2. Public Record Data attribute with Binary type
3. Record Name attribute with String type
4. Owner Name attribute with String type

You may specify attributes' names in one of two 2 ways (you may combine that ways in different entities).

Default names

The most simple way is to name attributes with default names because you don't need to map them in UserInfo.

Mapping via UserInfo

You can map your own attributes to the required service attributes. For each attribute you want to map, add an item to the attribute's UserInfo, using the key CloudCoreType and following values:

• Private Record Data value is privateRecordData.
• Public Record Data value is publicRecordData.
• Record Name value is recordName.
• Owner Name value is ownerName.

💡 Tips

• I recommend to set the Record Name attribute as Indexed, to speed up updates in big databases.
• Record Data attributes are used to store archived version of CKRecord with system fields only (like timestamps, tokens), so don't worry about size, no real data will be stored here.

CloudKit Sharing

To enable CloudKit Sharing when your entities have relationships, CloudCore will look for the following key:value pair in the UserInfo of your entities:

CloudCoreParent: name of the to-one relationship property in your entity

Example application

You can find example application at Example directory.

How to run it:

1. Set Bundle Identifier.
2. Check that embedded binaries has a correct path (you can remove and add again CloudCore.framework).
3. If you're using simulator, login at iCloud on it.

How to use it:

• + button adds new object to local storage (that will be automatically synced to Cloud)
• refresh button calls pull to fetch data from Cloud. That is useful button for simulators because Simulator unable to receive push notifications
• Use CloudKit dashboard to make changes and see it at application, and make change in application and see ones in dashboard. Don't forget to refresh dashboard's page because it doesn't update data on-the-fly.

Tests

CloudKit objects can't be mocked up, that's why I create 2 different types of tests:

• Tests/Unit here I placed tests that can be performed without CloudKit connection. That tests are executed when you submit a Pull Request.

• Tests/CloudKit here located "manual" tests, they are most important tests that can be run only in configured environment because they work with CloudKit and your Apple ID.

  Nothing will be wrong with your account, tests use only private CKDatabase for application.

  Please run these tests before opening pull requests. To run them you need to:

  1. Change TestableApp bundle id.
  2. Run in simulator or real device TestableApp target.
  3. Configure iCloud on that device: Settings.app → iCloud → Login.
  4. Run CloudKitTests, they are attached to TestableApp, so CloudKit connection will work.

Roadmap

• Properly push only changed fields from NSPersistenHistory
• Move beta to release status
• Add CloudCore.disable method
• Add methods to clear local cache and remote database
• Add error resolving for limitExceeded error (split saves by relationships).

Authors

deeje cooley, deeje.com

• added NSPersistentHistory and CloudKit Sharing Support

Vasily Ulianov, va...@me.com Open for hire / relocation.

• implemented version 1 and 2, with dynamic mapping between CoreData and CloudKit

Oleg Müller

• added full support for CoreData relationships