Basic data: error when deleting / adding objects

Question

Sometimes my application crashes when I want to update a Core Data file by downloading and analyzing a json file. I get the following error:

CoreData: Error: A serious application error. Excluded during processing of a master data change. This is usually a bug in the NSManagedObjectContextObjectsDidChangeNotification observer. - [__ NSCFSet addObject:]: try to insert nil with userInfo (null)

It doesn't matter where I store the NSManagedObjectContext in the iteration if I change the properties during the iteration?

here is my code:

- (void) updateData { dispatch_queue_t serialdQueue; serialdQueue = dispatch_queue_create("update", NULL); dispatch_async(serialdQueue, ^{ [self method1]; }); dispatch_async(serialdQueue, ^{ [self method2]; }); dispatch_async(serialdQueue, ^{ [self method3]; }); dispatch_async(serialdQueue, ^{ [self method4]; }); dispatch_async(serialdQueue, ^{ [self method5]; }); } -(void)method1 { //DOWNLOAD JSON FILE } -(void)method2 //here i add objects to the core data file { @try { for (NSDictionary *jsonActivity in [json objectForKey:@"Activities"]) { //ITERATE THROUGH JSON ACTIVITY ARRAY NSFetchRequest *request = [[NSFetchRequest alloc] init]; NSEntityDescription *entity = [NSEntityDescription entityForName:@"Activity" inManagedObjectContext:self.managedObjectContext]; [request setEntity:entity]; NSPredicate *searchFilter = [NSPredicate predicateWithFormat:@"title == %@", [jsonActivity objectForKey:@"title"]]; // CHECK IF OBJECT FROM JSON FILE ALREADY EXISTS... [request setPredicate:searchFilter]; NSError *error = nil; NSArray *results = [self.managedObjectContext executeFetchRequest:request error:&error]; if (error) { NSLog(@"Error %@", error); abort(); } if ([results count] == 0) { // ADD NEW ACTIVITY IF OLD LIST DOESNT CONTAIN IT Activity *activity = [NSEntityDescription insertNewObjectForEntityForName:@"Activity" inManagedObjectContext:self.managedObjectContext]; activity.title = [jsonActivity objectForKey:@"title"]; activity.remove = [NSNumber numberWithBool:NO]; // REMOVE FLAG = NO BECAUSE NEW OBJECTS AREN'T REMOVED } else { Activity *activity = (Activity*) [results objectAtIndex:0]; activity.remove = [NSNumber numberWithBool:NO]; // IF OBJECT ALREADY EXISTS IT SHOULD BE OBTAINED } AppDelegate *appDelegate = [[UIApplication sharedApplication] delegate]; [appDelegate saveContext]; // SAVE MO CONTEXT } } @catch (NSException *exception) { NSLog(@"Exception: %@", exception); } } -(void)method3 // DELETE OLD OBJECTS { NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init]; NSEntityDescription *entityDescription = [NSEntityDescription entityForName:@"Activity" inManagedObjectContext:self.managedObjectContext]; [fetchRequest setEntity:entityDescription]; NSPredicate *searchFilter = [NSPredicate predicateWithFormat:@"remove == %@", [NSNumber numberWithBool:YES]]; [fetchRequest setPredicate:searchFilter]; NSArray *objectsToDelete = [[NSArray alloc] init]; NSError *error = nil; objectsToDelete = [self.managedObjectContext executeFetchRequest:fetchRequest error:&error]; if (error) { NSLog(@"Error %@", error); abort(); } for (Activity *activity in objectsToDelete) { // DELETE OBJECTS WITH THE PROPERTY REMOVE = YES [self.managedObjectContext deleteObject:activity]; // DELETE ACTIVITY } AppDelegate *appDelegate = [[UIApplication sharedApplication] delegate]; [appDelegate saveContext]; // SAVE MO CONTEXT } -(void)method4 // CHANGE THE REMOVE PROPERTY TO YES OF ALL OBJECTS { NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init]; NSEntityDescription *entityDescription = [NSEntityDescription entityForName:@"Activity" inManagedObjectContext:self.managedObjectContext]; [fetchRequest setEntity:entityDescription]; NSArray *objects = [[NSArray alloc] init]; NSError *error = nil; objects = [self.managedObjectContext executeFetchRequest:fetchRequest error:&error]; if (error) { NSLog(@"Error %@", error); abort(); } for (Activity *activity in objects) { activity.remove = [NSNumber numberWithBool:YES]; } AppDelegate *appDelegate = [[UIApplication sharedApplication] delegate]; [appDelegate saveContext]; // SAVE MO CONTEXT NSLog(@"End Update"); } -(void)method5 //UPDATE UI { //UI UPDATES } 

Answer 1

You should not access the context of the managed entity on serialQueue . Take a look at the Concurrency section of NSManagedObjectContext .

If your context uses the NSPrivateQueueConcurrencyType or NSMainQueueConcurrencyType Concurrency type in your code, you can use one of the block-based methods to make sure that you are in the correct queue:

 //asyncrhonous [self.managedObjectContext performBlock:^{ //do stuff with the context }]; //syncrhonous [self.managedObjectContext performBlockAndWait:^{ //do stuff with the context }];