Core data + CloudKit - sharing between iOS and watchOS companion app

Question

In my app I store data with core data. Recently I discovered the new feature introduced by Apple in WWDC19 which allows core data to work with CloudKit. I just enabled cloudKit for my app and used an NSPersistentCloudKitContainer instead of NSPersistentContainer and all was set up ! All my data is shared between ios devices. That works like NSPersistentContainer but it sends a copy of changes on icloud server, so there is always a local cache of data.

Now I'd like to access that data from my apple watch companion app but not all the data, only a specific entity! So how could I do that? I tried to set the NSPersistentCloudKitContainer shared between both targets with the attribut inspector but watch don't get any data. I can see in cloudKit dashboard there are requests from watchOS but watch just don't get any data.

But if I save an entity from the watch to core data I can get it only from the watch. My conclusion is both are no storing the data at the same place. So how could I fix that? There are already using the same NSPersistendCloudKitContainer.

the container shared between both targets :

import Foundation
import CoreData

public class CoreDataContainer {
    lazy var persistentContainer: NSPersistentContainer = {
        /*
         The persistent container for the application. This implementation
         creates and returns a container, having loaded the store for the
         application to it. This property is optional since there are legitimate
         error conditions that could cause the creation of the store to fail.
         */
        let container = NSPersistentCloudKitContainer(name: "MyProjectName")
        container.loadPersistentStores(completionHandler: { (storeDescription, error) in
            if let error = error as NSError? {
                // Replace this implementation with code to handle the error appropriately.
                // fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.

                /*
                 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("Unresolved error \(error), \(error.userInfo)")
            }
        })
        return container
    }()

    // MARK: - Core Data Saving support

    func saveContext () {
        let context = persistentContainer.viewContext
        if context.hasChanges {
            do {
                try context.save()
            } catch {
                // Replace this implementation with code to handle the error appropriately.
                // fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
                let nserror = error as NSError
                fatalError("Unresolved error \(nserror), \(nserror.userInfo)")
            }
        }
    }
}

Answer 1

Resolved by adding a cloudKitContainerOptions to my context description like this :

class CoreDataStack {
    static let persistentContainer: NSPersistentCloudKitContainer = {
        let container = NSPersistentCloudKitContainer(name: "MyProjectName")
        let description = container.persistentStoreDescriptions.first

        description?.cloudKitContainerOptions = NSPersistentCloudKitContainerOptions(containerIdentifier: "myCloudContainerID") // HERE !

        container.loadPersistentStores(completionHandler: { (_, error) in
            if let error = error as NSError? {
                fatalError("Unresolved error \(error), \(error.userInfo)")
            }
        })
        return container
    }()  

}