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copied!<p>The correct way to achieve this sort of thing is with a new managed object context. You create a managed object context with the same persistent store:</p> <pre><code>NSManagedObjectContext *tempContext = [[[NSManagedObjectContext alloc] init] autorelease]; [tempContext setPersistentStore:[originalContext persistentStore]]; </code></pre> <p>Then you add new objects, mutate them, etc.</p> <p>When it comes time to save, you need to call [tempContext save:...] on the tempContext, and handle the save notification to merge that into your original context. To discard the objects, just release this temporary context and forget about it. </p> <p>So when you save the temporary context, the changes are persisted to the store, and you just need to get those changes back into your main context:</p> <pre><code>/* Called when the temp context is saved */ - (void)tempContextSaved:(NSNotification *)notification { /* Merge the changes into the original managed object context */ [originalContext mergeChangesFromContextDidSaveNotification:notification]; } // Here's where we do the save itself // Add the notification handler [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(tempContextSaved:) name:NSManagedObjectContextDidSaveNotification object:tempContext]; // Save [tempContext save:NULL]; // Remove the handler again [[NSNotificationCenter defaultCenter] removeObserver:self name:NSManagedObjectContextDidSaveNotification object:tempContext]; </code></pre> <p>This is also the way you should handle multi-threaded core data operations. One context per thread.</p> <p>If you need to access existing objects from this temporary context (to add relations etc.) then you need to use the object's ID to get a new instance like this:</p> <pre><code>NSManagedObject *objectInOriginalContext = ...; NSManagedObject *objectInTemporaryContext = [tempContext objectWithID:[objectInOriginalContext objectID]]; </code></pre> <p>If you try to use an <code>NSManagedObject</code> in the wrong context you will get exceptions while saving.</p>

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