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You're not supposed to modify the collection being iterated upon with fast enumeration, but I'm not really sure to what extent that is. The below code has not caused me any problems, but I'm not sure if it was me being lucky. Does anyone have a defininite answer?

for(NSManagedObject *myObject in myArray) {
   [myObject.managedObjectContext deleteObject:myObject];
}

So I'm not really modifying the array, but I am deleting the object from the context, which might just indirectly modify the array, but I'm not sure on that..

Snowman
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1 Answers1

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You can do anything you want with the objects in the array, so long as you do not mutate the array itself.

That code is perfectly acceptable.

Note, however, if you have lots of objects to delete, you should consider other things as well (like prefetching relationships, using an autorelease pool, making sure your MOC stays clean, etc.)

Jody Hagins
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  • What do you mean by "making sure your MOC stays clean"? – Snowman Sep 02 '12 at 21:05
  • When you do very large deletions, you want to fetch objects, then delete them to reduce trips to the database. If it's a lot, you want to do it in smaller batches, and make sure the MOC releases deleted objects (via reset or refresh with NO). Once saved, you also want to make sure all referencing objects are gone so you don't refer to deleted objects. – Jody Hagins Sep 02 '12 at 21:08
  • But wouldn't deleting the item from the context cause it to go missing from the array, in turn modifying it? – Snowman Sep 02 '12 at 21:18
  • The object is deleted in the MOC, and not committed until you save. In either event, the array you have still has all its objects. The objects may be deleted in the MOC, and even after saving, they may be totally deleted, but the array itself is still unchanged. – Jody Hagins Sep 02 '12 at 21:52