title: Core Data mergeChangesFromContextDidSaveNotification Performance
body: <p>I am importing large amounts of data on a background queue. Each <code>Route</code> has few thousand <code>Location</code>s.</p>
  
  <p>I am importing on a <code>NSPrivateQueueConcurrencyType</code>.</p>
  
  <p>In the following method I am getting every object I created i.e. Routes and Locations.</p>
  
  <pre><code>- (void)contextDidSave:(NSNotification*) notification
  </code></pre>
  
  <p>This means that I have a huge number of objects that need to be <code>mergeChangesFromContextDidSaveNotification</code>ed on the main thread although, initially, I only need the Routes and possible not even those.</p>
  
  <p>How can I skip merging objects when they are of no interest, such as when no fetch request has yet been made?</p>
  
  <p>How can I merge just the <code>Route</code>s and when I need the <code>Location</code>s let them be lazy loaded?</p>