Question

I am having an issue with Core Data in a background GCD thread… I want to update a record, but after fetching it and setting the values it doesn’t seem to actually save the updated record.

isUpdate is a BOOL I have setup that tells me whether I am running a first time parse/save or whether it’s a record I need to update. In my case, when I update a record it doesn’t actually seem to update in my store.

I’m using MagicalRecord helpers. Here’s my code:

// Create background context
NSManagedObjectContext *backgroundContext = [[NSManagedObjectContext alloc] init];
[backgroundContext setPersistentStoreCoordinator:[NSPersistentStoreCoordinator defaultStoreCoordinator]];
// Save the background context and handle the save notification
[[NSNotificationCenter defaultCenter] addObserver:self
                                         selector:@selector(backgroundContextDidSave:)
                                             name:NSManagedObjectContextDidSaveNotification
                                           object:backgroundContext];

// Parsing data...
//..

Record *record;
if (!isUpdate) {
    record = [NSEntityDescription insertNewObjectForEntityForName:@"Record" inManagedObjectContext:backgroundContext];
} else {
    NSPredicate *recordPredicate = [NSPredicate predicateWithFormat:@"SELF.tag == %@", [[node attributeForName:@"tag"] stringValue]];
    record = [Record findFirstWithPredicate:recordPredicate];
}
[record setTitle:[[recordNode attributeForName:@"title"] stringValue]];

// Parsing other data...
//..

NSError *error = nil;
// save the context
[backgroundContext save:&error];
if (error) {
    NSLog(@"An error occurred: %@", error);
}

And here’s the notification:

- (void)backgroundContextDidSave:(NSNotification *)notification {
    // Make sure we're on the main thread when updating the main context
    if (![NSThread isMainThread]) {
        [self performSelectorOnMainThread:@selector(backgroundContextDidSave:)
                           withObject:notification
                        waitUntilDone:NO];
        return;
    }
    // merge in the changes to the main context on the main thread
    [[NSManagedObjectContext defaultContext] mergeChangesFromContextDidSaveNotification:notification];
}

Answer 1

You are mixing two contexts. This code is probably bad:

 record = [Record findFirstWithPredicate:recordPredicate];

I assume that this finds record in different context instead of Your backgroundContext. You should change it to something like this:

 record = [Record findFirstWithPredicate:recordPredicate inManagedObjectContext:backgroundContext];