CKFetchRecordChangesOperation

Use this type of operation object to optimize fetch operations for locally managed sets of records. Specifically, use it when you maintain a local cache of your record data and need to synchronize that cache periodically with the server.

To get the most benefit out of a CKFetchRecordChangesOperation object, you must maintain a local cache of the records from the specified zone. Each time you fetch changes from that zone, the server provides a token that identifies your request. With each subsequent fetch request, you initialize the operation object with the token from the previous request, and the server returns only the records that changed since that request.

The blocks you assign to process the fetched records are executed serially on an internal queue managed by the operation. Your blocks must be capable of executing on a background thread, so any tasks that require access to the main thread must be redirected accordingly.

If you assign a completion block to the completionBlock property of the operation object, the completion block is called after the operation executes and returns its results to you. You can use a completion block to perform housekeeping chores related to the operation, but do not use it to process the results of the operation itself. Any completion block you specify should be prepared to handle the failure of the operation to complete its task, whether due to an error or an explicit cancellation.