Question

I am encountering an issue when attempting to remove an object from my Core Data store. The error I receive when calling deleteOject is as follows: An NSManagedObjectContext cannot delete objects in other contexts.

I have found some documentation regarding this error online but it mostly relates to accessing the ManagedObjectContext in multiple threads which can cause issues, but I am not currently working on any other threads. I have gone through my code in an attempt to ensure that I am not creating any other context except for the one that I create in my AppDelegate and can not find a likely culprit.

The code that I am testing with is below:

NSMutableSet *remoteNids = [NSMutableSet setWithObjects:@"140", @"141", nil];
for (GCEvent *event in nodeEventsFromStore) {
    if (![remoteNids containsObject:event]) {
        NSLog(@"Event no longer exists on remote. Removing object %@ from store.", event);
        [[delegate managedObjectContext] deleteObject:event];
    }
    else {
        NSLog(@"Event %@ exists on remote", event);
    }
}

Answer 1

It’s highly unlikely that Core Data is lying to you. I would suggest putting an assert in your code like this:

NSAssert([delegate managedObjectContext] == [event managedObjectContext], @"Found two contexts: %@ and %@", [delegate managedObjectContext, [event managedObjectContext]);

Run your app via Xcode with breakpoints on (so it breaks when you hit the assertion) and set MallocStackLoggingNoCompact=YES.

When the assert is triggered, you can use the gdb console like so:

(gdb) info malloc [address of event's MOC]
(gdb) info malloc [address of delegate MOC]

That will print the alloc stack trace and show you where you created the two moc’s.