Core Data/NSOperation: crash while enumerating through and deleting objects

Question

I have a core data based app that has a one object (a list) to many objects (list items) relationship. I\'m working on syncing data between devices, and as part of that I im

Answer 1

There is a bit of a clue in the error message, where you can see the class NSFaultingMutableSet listed. Indeed the set you are enumerating is really just a proxy for the to-many relationship that will potentially load data on demand. Since items in the collection are being marked as deleted during the enumeration, the possibility exists that some of the collection will 'change' while you're enumerating it and you'll see that error.

A common way to deal with this is to create a copy of the collection and enumerate the copy. The naive approach to that would just be:

NSSet *iterItems = [[list.items copy] autorelease];
for (ListItemCD *item in iterItems) { ... }

But I've found when dealing with Core Data that -copy does not actually return a copy but often just another faulting proxy. So I instead choose to copy the collection this way:

NSSet *iterItems = [NSSet setWithSet:list.items];
for (ListItemCD *item in iterItems) { ... }