title: CloudKit: CKFetchRecordChangesOperation, CKServerChangeToken and Delta Download
body: <p>My question is related to the "Delta Download" thing as it was named in WWDC 2014 Advanced CloudKit.</p>
  
  <p>I'm trying to make syncronization for my Core Data app, which is iPhone only for now (think: there is only one device active). So, basically the app will store user records in the cloud from one same device, for the most cases for now.</p>
  
  <p>I have trouble with understanding custom zone feature which is based on <code>CKFetchRecordChangesOperation</code> aka Delta Download.</p>
  
  <p>As I got it right, we have <code>CKServerChangeToken</code>'s to maintain sync operations (I mean download only those records which was added/modified/deleted by another device), as was presented on WWDC.
  But, what I can't understand is that we recieve that token only after <code>CKFetchRecordChangesOperation</code>, when we save records to the cloud we don't get new token.</p>
  
  <p>And if we make fetch with the current available token (since it changes only after fetch), we recieve records that was saved from our previous save operation. Basicaly we get save recods that already have on our device. Why? I'm missing something here?</p>
  
  <p>What if we seeding some data to the cloud (from device A), it is justified for situation when device B is fetching the zone records, but what if device A be? Download all the records again?</p>
  
  <p>I found <code>recordChangeTag</code> in the <code>CKRecord</code>, is this a property I can use for resolving conflicts with local objects - fetched objects (same or different version), if so can somebody give me example of how I need to do this: save recordChangeTag to Core Data when save record to CloudKit for the first time or how?</p>
  
  <p>The lack of documentation is such a headache.</p>