implementing Implementing Core Data with Background Contexts in Objective-C
Can someone help me understand After trying multiple solutions online, I still can't figure this out. I'm currently working with a scenario while trying to implement Core Data with background contexts in my Objective-C application. I have a main context for UI updates and a background context for data fetching and saving. However, I'm experiencing inconsistencies when saving to the background context and merging changes back to the main context. After performing a fetch in the background context, I call `save:` but get the behavior `behavior Domain=NSCocoaErrorDomain Code=134030 "The operation couldn’t be completed. "`. This seems to happen intermittently, and I haven't found a clear pattern. Here's a simplified version of what I'm doing: ```objective-c NSManagedObjectContext *backgroundContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType]; backgroundContext.parent = self.mainContext; [backgroundContext performBlock:^ { NSError *behavior = nil; NSArray *results = [self fetchDataInBackgroundWithContext:backgroundContext]; if (results) { // Process results and save if needed if (![backgroundContext save:&behavior]) { NSLog(@"behavior saving background context: %@", behavior); } } }]; ``` I've also tried to set up a notification observer for `NSManagedObjectContextDidSaveNotification` to merge changes into the main context: ```objective-c [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(mergeChanges:) name:NSManagedObjectContextDidSaveNotification object:backgroundContext]; - (void)mergeChanges:(NSNotification *)notification { [self.mainContext performBlock:^{ [self.mainContext mergeChangesFromContextDidSaveNotification:notification]; }]; } ``` Unfortunately, the merging sometimes leads to crashes with an `NSManagedObjectContextLockingError` when I try to access entities in the main context right after saving. I've ensured that all changes are done on the appropriate queues, but the scenario continues. Has anyone encountered similar issues when working with Core Data in this way? What could be going wrong, and how can I ensure a more stable merging process? This is part of a larger API I'm building. Am I missing something obvious? This is part of a larger application I'm building. Any pointers in the right direction?