ax-core-data

Core Data

Quick Patterns

Stack Setup

class CoreDataStack {
    static let shared = CoreDataStack()

    lazy var persistentContainer: NSPersistentContainer = {
        let container = NSPersistentContainer(name: "MyModel")
        container.loadPersistentStores { _, error in
            if let error { fatalError("Core Data failed: \(error)") }
        }
        container.viewContext.automaticallyMergesChangesFromParent = true
        container.viewContext.mergePolicy = NSMergeByPropertyObjectTrumpMergePolicy
        return container
    }()

    var viewContext: NSManagedObjectContext {
        persistentContainer.viewContext
    }
}

CloudKit Integration

lazy var persistentContainer: NSPersistentCloudKitContainer = {
    let container = NSPersistentCloudKitContainer(name: "MyModel")

    let publicDescription = NSPersistentStoreDescription()
    publicDescription.cloudKitContainerOptions =
        NSPersistentCloudKitContainerOptions(
            containerIdentifier: "iCloud.com.myapp"
        )
    publicDescription.cloudKitContainerOptions?.databaseScope = .public

    container.persistentStoreDescriptions = [publicDescription]
    container.loadPersistentStores { _, error in
        if let error { fatalError("CloudKit Core Data failed: \(error)") }
    }
    container.viewContext.automaticallyMergesChangesFromParent = true
    return container
}()

Background Context Operations

// CRITICAL: NSManagedObject is NOT thread-safe
// Never pass managed objects across threads - use objectID

func importData(_ items: [RawItem]) {
    let context = persistentContainer.newBackgroundContext()
    context.mergePolicy = NSMergeByPropertyObjectTrumpMergePolicy

    context.perform {
        for item in items {
            let entity = CDTrack(context: context)
            entity.id = item.id
            entity.title = item.title
        }

        do {
            try context.save()
        } catch {
            context.rollback()
        }
    }
}

// Pass objectID across threads
func updateOnBackground(objectID: NSManagedObjectID) {
    let context = persistentContainer.newBackgroundContext()
    context.perform {
        let object = context.object(with: objectID) as! CDTrack
        object.playCount += 1
        try? context.save()
    }
}