Saving Modified Data in CloudKit - ios

Question

I have been testing out CloudKit as i wish to release an app using it when the release of iOS8 occurs. It seems simple enough to save data using the code below:
CKRecordID * recordID = [[CKRecordID alloc] initWithRecordName:#"basicRecord"];
CKRecord * record = [[CKRecord alloc] initWithRecordType:#"basicRecordType" recordID:recordID];
[record setValue:#"defaultValue" forKey:#"defaultKey"];
CKDatabase *database = [[CKContainer defaultContainer] publicCloudDatabase];
[database saveRecord:record completionHandler:^(CKRecord *record, NSError *error) {
if (error) {
NSLog(#"Error: %#", error);
} else {
NSLog(#"Record Saved!");
}
}];
and I receive no errors from this. However, if i try to run the code again, maybe because i have changed the record value to
[record setValue:#"newValue" forKey:#"defaultKey"];
I receive an error which begs the question, how do i go about saving a modified piece of data. After all, this is a fundamental part of saving things to the cloud. The error is below and any help would be greatly appreciated, don't hesitate to ask for further information.
Error: <CKError 0x17024afb0: "Server Record Changed" (14/2017); "Error saving record <CKRecordID: 0x144684a80; basicRecord:(_defaultZone:__defaultOwner__)> to server: (null)"; uuid = 182C497F-966C-418A-9E6A-5563BA6CC6CD; container ID = "iCloud.com.yourcompany.CloudKit">

Answer 1

This error is probably because saveRecord: works only for new records or records that are newer than the version on the server:
This method saves the record only if it has never been saved before or if it is newer than the version on the server. You cannot use this method to overwrite newer versions of a record on the server. CKDatabase docs
The recommended approach to modify an existing record (or set of records) is to use a CKModifyRecordsOperation set with the desired savePolicy to deal with conflicts:
After modifying the fields of a record, use this type of operation object to save those changes to a database. (...)
When saving records, the value in the savePolicy property determines how to proceed when conflicts are detected on the server. CKModifyRecordsOperation docs

Answer 2

From the docs of CKRecord:
New records exist only in memory until you explicitly save them to iCloud.
When you set the new value [record setValue:#"newValue" forKey:#"defaultKey"]; you have already saved the record, making it invalid.
You can use CKModifyRecordsOperation and in most situations it might be preferrable but you don't have to. Just fetch your data using a fresh CKRecord, then feed that record into saveRecord: as described here.

Answer 3

After you save the record, fetch it so that the retured record will then have the RecordID that Cloudkit added
Then on that same fetched record, use setValue to change the data you want to change
Then you can use CFModifyRecordsOperation
In the example below, cachedCKRecordsServiceCenter contains the fetched records from cloudkit and those records have the CloudKit RecordID's in them......
//find this service center in the cached records
for (_,serviceCenter) in (theModel?.cachedCKRecordsServiceCenter.enumerated())! //is data for logged in Co ONLY with NO Co name attached
{
let name = serviceCenter["name"] as! String
returnValue = "Try Again"
if name == displayedRecordName
{
serviceCenter.setValue(displayedRecordName! + "_" + (theModel?.companyName)!, forKey: "name") //db values have Co name appended
serviceCenter.setValue(label2Text.text, forKey:"street1")
serviceCenter.setValue(label3Text.text, forKey:"street2")
serviceCenter.setValue(label4Text.text, forKey:"city")
serviceCenter.setValue(label5Text.text, forKey:"state")
serviceCenter.setValue(label6Text.text, forKey:"zip")
serviceCenter.setValue(label7Text.text, forKey:"phone")
serviceCenter.setValue(label8Text.text, forKey:"email")
serviceCenter.setValue(label9Text.text, forKey:"note")
let saveRecordsOperation = CKModifyRecordsOperation()
var ckRecordsArray = [CKRecord]()
// set values to ckRecordsArray
ckRecordsArray.append(serviceCenter)
saveRecordsOperation.recordsToSave = ckRecordsArray
saveRecordsOperation.savePolicy = .ifServerRecordUnchanged
appDelegate.locked = true
saveRecordsOperation.modifyRecordsCompletionBlock = { savedRecords, deletedRecordIDs, error in
if error != nil {
// Really important to handle this here
////////print("ERROR: Unable to update Driver Location: Error= \(error)")
self.returnValue = "ERROR: Unable to update Driver Location: ERROR = \(error)"
self.appDelegate.locked=false
}
else
{
////print("Successfully updated Service Center")
self.appDelegate.locked=false
self.returnValue = "Successfully updated Service Center"
self.appDelegate.locked=false
//reget the data into the cach
self.theModel?.fetchServiceCenterFromCloudKit1()
}
}
CKContainer.default().publicCloudDatabase.add(saveRecordsOperation)
}
}