The order in which iCloud records are modified

I'm now using CKModifyRecordsOperation to add 5 records to iCloud. My code is like this:

let recordsToSave: [CKRecord] = [record1, record2, record3, record4, record5]
let operation = CKModifyRecordsOperation(recordsToSave: recordsToSave, recordIDsToDelete: [])

After successfully modifying the 5 records, I use CKQueryOperation to query all records, my code is like this:

let predicate = NSPredicate(value: true)
let query = CKQuery(recordType: RECORDTYPE, predicate: predicate)
query.sortDescriptors = [NSSortDescriptor(key: "modificationDate", ascending: true)]
let operation = CKQueryOperation(query: query)

I thought the order of the fetched records would be record1-record2-record3-record4-record5.

But, actually, the order is chaotic. It might be 1-3-5-4-2, or it might be 2-4-5-1-3, or any other. It depends on iCloud itself. But I checked these 5 records in iCloud Dashboard, these 5 records's modifation date are the same.

Is there any way to achieve the order I want?

Solution

When databases are sorting on a particular property, they will generally return records that have the same value for that property in an arbitrary order, for performance reasons. If you need to have that order preserved for those records, you could do one of two things:

Add a secondary ID property which you set for each record in that modify operation, and add a second NSSortDescriptor on that property. (in your example, you would set the value of this property for record1 to 1, record2 to 2, and so on)
Modify the records one at a time so that they receive unique modification times.

Not knowing more specific details about your app, I would lean towards the secondary ID solution. If you don't want to make your database more complicated, and your app wouldn't be modify huge batches of records at one time, the latter solution may be more appropriate.