Core Data: Deleting causes 'NSObjectInaccessibleException' from NSOperation with a reference to a deleted object

Question

My application has NSOperation subclasses that fetch and operate on managed objects. My application also periodically purges rows from the database, which can result in the following race condition:

• An background operation fetches a bunch of objects (from a thread-specific context). It will iterate over these objects and do something with their properties.
• A bunch of rows are deleted in the main managed object context.
• The background operation accesses a property on an object that was deleted from the main context. This results in an 'NSObjectInaccessibleException', reason: 'CoreData could not fulfill a fault'

Ideally, the objects that are fetched by the NSOperation can be operated on even if one is deleted in the main context. The best way I can think to achieve this is either to:

• Call [request setReturnsObjectsAsFaults:NO] to ensure that Core Data won't try to fulfill a fault for an object that no longer exists in the main context. The problem here is I may need to access the object's relationships, which (to my understanding) will still be faulted.
• Iterate through the managed objects up front and copy the properties I will need into separate non-managed objects. The problem here is that (I think) I will need to synchronize/lock this part, in case an object is deleted in the main context before I can finish copying.

Am I missing something obvious? It doesn't seem like what I'm trying to accomplish is too out of the ordinary. Thanks for your help.

Answer 1

I ended up mitigating this by perform both fetches and deletes on the same queue.