title: Core Data: Save unique object ID
body: <p>I see that there is a method of getting the unique id of a managed object:</p>
  
  <pre><code>NSManagedObjectID *moID = [managedObject objectID];
  </code></pre>
  
  <p>But, as I have read, that changes when it is saved.</p>
  
  <p>What is a better way of creating my own unique ID and saving it in each object, making sure that it IS unique and does't change?</p>