title: Core Data server syncing
body: <p>I have a dilemma regarding Core Data and syncing data with server. 
  I wrote an app which uses Core Data, don't use id attributes, everything is set with relationships. Most of data is being generated on device and should be sent to server as backup. On the other hand, there is some data that can be reused among users and I want to have control over it, i.e. modifying, deleting, adding.</p>
  
  <p><strong>Question</strong><br>
  When sending data to server, what's prefered way of dealing with relationships? In my opinion, it would be very inefficient to think in terms of Core Data, sending all relation objects to server and then deal with them if they already exist on server. So, using uniqueId is obligatory? Generating ones on server which will be shared and others on devices? Is there any other approach?  </p>
  
  <p>Thank you.</p>