In this example, we will solve the case of having to update a setting of the App, like the server URL and its API key.

Swift - CloudKit: Update App Settings

See: https://www.invasivecode.com/weblog/advanced-cloudkit-i

01. To access the schema of the database, click on the button CloudKit Dashboard, or 
go to https://icloud.developer.apple.com/dashboard. In the CloudKit dashboard, you 
can manage the schema of the database, create new Record Types, and add, edit and delete records.

02. Select Record Types and then click on the + button to create a new record type. 
Name the new record type WebServiceSettings. Then, add two fields of type string. 
Call them serviceURL and serviceAPIKey. By default, when you create new fields, 
indexes are added, to allow sorting, querying and searching on them. In this case, 
we can uncheck all of them as we are only going to perform direct fetches of a record 
based on its record name.

03. Now, select Default Zone, chose WebServiceSettings from the popup menu, and click on 
the New Record button to add a new record. In the Record Name field, type a unique 
identifier. We will use that identifier to fetch the record from the App. By default, 
the dashboard gives you one like 99cae8ed-274e-4f56-87d2-83b27180c3fb, but you can use 
any name record you want, as long as it is unique across this database. I am going to 
use awesomeWebService for this example. Now, type a URL and an API key in the record 
fields, and click on the Save button.

04. Let’s go back to Xcode. In the AppDelegate.swift, add this method and then call it when 
your App launches:

func updateWebServiceSettings() {
    let publicDatabase = CKContainer.defaultContainer().publicCloudDatabase
    let recordID = CKRecordID(recordName: "awesomeWebService")
    publicDatabase.fetchRecordWithID(recordID) { (record: CKRecord?, error: NSError?) -> Void in
        guard error == nil else {
            return
        }
 
        // Update the local copy of the settings
        if let localRecord = record,
            let urlString = localRecord["serviceURL"] as? String,
            let apiKey = localRecord["serviceAPIKey"] as? String {
                self.updateSettingsWithServiceURL(NSURL(string: urlString)!, serviceApiKey:apiKey )
        }
    }
}
 
func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
    updateWebServiceSettings()
    return true
}

05. As you can see in the above source code, we are just getting a reference to the 
public database. Then we create a recordId with the name of the record we are interested 
in (remember that this id is unique). And finally, we tell the public database to perform 
a fetch of that record. If the fetch succeeds, we get back an instance of the CKRecord 
class with the values of its fields. At this point, you should update your local copy 
of the data with the new values.