Data Sync Problem After Support Cloud Kit for Core Data

I recently utilized Core Data as the local persistence layer for my side project and discovered its compatibility with CloudKit for remote storage. Given that both Core Data and CloudKit are offerings from Apple, I was eager to test their integration. However, after following the WWDC demo on migrating from NSPersistentContainer to NSPersistentCloudKitContainer, I encountered unexpected challenges. The most significant, and surprisingly unmentioned, issue was the all my existing data did not sync to the cloud after transitioning to the CloudKit container.

Imagine the frustration of discovering your data isn’t syncing correctly across devices. When I looked online, I found others confronting the same issue. A critical step to address this is to set NSPersistentHistoryTrackingKey to true when configuring your NSPersistentContainer. This allows CoreData to track persistent history, facilitating the migration of your existing data to the CloudKit container.

However, according to the forum discussion posted above, this modification is not enough to ensure your data intact. @andrewbuilder listed multiple scenarios incurred by various settings and he manifested that:

Records entered prior to setting NSPersistentHistoryTrackingKey = true are never synced to users CloudKit account and remain only on the device on which they are created.

That really sucks… 🤮

Dmitry Deplov handled this issue by copying all existing data to a new context. He then saved this data to a new cloud container before removing the old one. This approach acts as a workaround to ensure proper data transformation.

After all these efforts, it sets me thinking that when implementing a new feature, even if it’s provided by Apple, don’t assume seamless integration. Despite official documentation, there are often many missing pieces, leaving developers to craft their own solutions.