title: CoreData merging data from two different contexts
body: <p>I am updating my core data in a background thread. I've setup the policy. THe updater class updates and saves the data.</p>
  
  <pre><code>NSManagedObjectContext *defaultContext = [(AppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext];
  
      dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{
  
          NSManagedObjectContext *context = [[NSManagedObjectContext alloc] init];
          [context setPersistentStoreCoordinator:[defaultContext persistentStoreCoordinator]];
          [context setMergePolicy:NSMergeByPropertyObjectTrumpMergePolicy];               //step 2
          [defaultContext setMergePolicy:NSMergeByPropertyStoreTrumpMergePolicy];
  
          Updater *updater = [[Updater alloc] initWithUsername:@"test2" 
                                                      password:@"test2"];
          [updater setContext:context];
          [updater update];
          [updater release];
  
          [self setUpdating:NO];
  
          dispatch_sync(dispatch_get_main_queue(), ^{
              completion();
          });
      });
  </code></pre>
  
  <p>My friend told me that i need some sort of notification to notify my original default context to update the data. Do I need that? Or what I have done will suffice? If so, how would i go about doing that?</p>