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