jazzedge

See: https://developer.apple.com/library/content/documentation/DataManagement/Conceptual/CloudKitQuickStart/SubscribingtoRecordChanges/SubscribingtoRecordChanges.html

01. Save Subscriptions to the Database

In your code, create a subscription object specifying the record type, predicate, and types of changes you 
want to be notified about. Then save the subscription object to the database.

To create and save a subscription

A. Create a predicate object.

jazzedge

See: https://developer.apple.com/library/content/documentation/DataManagement/Conceptual/CloudKitQuickStart/AddingAssetsandLocations/AddingAssetsandLocations.html

01. Store Large Files in CloudKit

You can store large data files in CloudKit using the Asset field type. Assets are owned by the associated 
record, and CloudKit handles garbage collection for you. CloudKit also efficiently uploads and downloads 
assets.

In code, the Asset field type is represented by a CKAsset object. This code fragment sets an Asset field 
in an Artwork record to a resource file.

jazzedge

See: https://developer.apple.com/library/content/documentation/DataManagement/Conceptual/CloudKitQuickStart/CreatingaSchemabySavingRecords/CreatingaSchemabySavingRecords.html

Improve the user’s experience by verifying that the user is signed in to their iCloud account 
before saving records. If the user is not signed in, present an alert instructing the user how 
to enter their iCloud credentials and enable iCloud Drive. 

Insert your code that saves records in the else clause below.

CKContainer.default().accountStatus(completionHandler: {(_ accountStatus: CKAccountStatus, _ error: Error?) -> Void in
    if accountStatus == .noAccount {

jazzedge

To run your app in iOS Simulator, enter the iCloud credentials in iOS Simulator
before you select the simulator and click the Run button in Xcode. You need to 
perform these steps for each iOS Simulator you select in the Scheme pop-up menu in Xcode.

To enter iCloud credentials in iOS Simulator

Choose Xcode > Open Developer Tool > iOS Simulator.
In iOS Simulator, choose Hardware > Home.
Launch the Settings app and click iCloud.
../Art/3_icloud_settings_2x.png

jazzedge

See: https://developer.apple.com/library/content/documentation/DataManagement/Conceptual/CloudKitQuickStart/CreatingaSchemabySavingRecords/CreatingaSchemabySavingRecords.html

See: https://developer.apple.com/library/content/documentation/DataManagement/Conceptual/CloudKitQuickStart/AddingReferences/AddingReferences.html

You can use reference field types to represent both one-to-one and one-to-many relationships between
your model objects. In your code, a reference field is a CKReference object that encapsulates the 
record ID for a target record and is added to the source record. To represent a one-to-one relationship 
in your schema, add a reference field to the source record type.

To represent a one-to-many relationship between your model objects, it is more efficient if the reference 

jazzedge

The table shows possible field types, as they appear in CloudKit Dashboard,
and their equivalent CloudKit framework classes.

Field Type
Class
Description

Asset
CKAsset
A large file that is associated with a record but stored separately

jazzedge

You’ll need an iCloud account to save records to a CloudKit container. 
You’ll enter the credentials for this iCloud account on the device that you run your app. 
If you don’t have an iCloud account, create one that you can use during development. 
On your Mac, launch System Preferences and click iCloud. Click Create Apple ID under the 
Apple ID text field and follow the instructions.

In development, when you run your app through Xcode on a simulator or a device, you need to 
enter iCloud credentials to read records in the public database. In production, the default 
permissions allow non-authenticated users to read records in the public database but do not 
allow them to write records.

jazzedge

See: https://developer.apple.com/library/content/documentation/DataManagement/Conceptual/CloudKitQuickStart/EnablingiCloudandConfiguringCloudKit/EnablingiCloudandConfiguringCloudKit.html#//apple_ref/doc/uid/TP40014987-CH2-SW1

01. Add Containers to an App

Select an existing container ID used by another app or create a new one.

To add a container to an app

A. In the Capabilities pane under the iCloud settings, select “Specify custom containers.”
When you previously selected the CloudKit service, Xcode created a default container ID for your 

jazzedge

Within the scope of an application’s cloud container, each user has a unique, application 
specific iCloud user ID and a user info record where the user ID is used as the record ID 
for the user’s info record.
The record ID of the current user’s info record can be obtained via a call to the 
fetchUserRecordID(completionHandler:) method of the container instance. Once the record 
ID has been obtained, this can be used to fetch the user’s record from the cloud database:

container.fetchUserRecordID(completionHandler: {recordID,    

jazzedge

See: https://www.whatmatrix.com/blog/a-guide-to-cloudkit-how-to-sync-user-data-across-ios-devices/

01. Creating a Custom Zone

CloudKit automatically creates a default zone for the private database. However, you can get 
more functionality if you use a custom zone, most notably, support for fetching incremental record changes.

Since this is a first example of using an operation, here are a couple of general observations:

First, all CloudKit operations have custom completion closures (and many have intermediate closures,