When does Core Data save the managed object context by itself?

Question

I have a OS X 10.9 only, non-document application.
When i do not call -save: explicitly on my managed object context, when does Core Data call -save: by itself?
Up to now, i have only found out, that it saves before quitting the application.

Answer 1

if you checked "Core Data" when creating a new Xcode project, this should be found i your app delegate:

- (void)applicationWillTerminate:(UIApplication *)application {
    // Called when the application is about to terminate. Save data if appropriate. See also applicationDidEnterBackground:.
    // Saves changes in the application's managed object context before the application terminates.
    [self saveContext];
}

#pragma mark - Core Data Saving support

- (void)saveContext {
    NSManagedObjectContext *managedObjectContext = self.managedObjectContext;
    if (managedObjectContext != nil) {
        NSError *error = nil;
        if ([managedObjectContext hasChanges] && ![managedObjectContext save:&error]) {
            // Replace this implementation with code to handle the error appropriately.
            // abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
            NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
            abort();
        }
    }
}

So when terminating the app it will explicitly call save.

The right answer is: The context will only be saved when you call save: on it. But with the xcode template this is set up for you.

---

The code above is for iOS, for Mac OS X it looks like

- (NSApplicationTerminateReply)applicationShouldTerminate:(NSApplication *)sender {
    // Save changes in the application's managed object context before the application terminates.

    if (!_managedObjectContext) {
        return NSTerminateNow;
    }

    if (![[self managedObjectContext] commitEditing]) {
        NSLog(@"%@:%@ unable to commit editing to terminate", [self class], NSStringFromSelector(_cmd));
        return NSTerminateCancel;
    }

    if (![[self managedObjectContext] hasChanges]) {
        return NSTerminateNow;
    }

    NSError *error = nil;
    if (![[self managedObjectContext] save:&error]) {

        // Customize this code block to include application-specific recovery steps.              
        BOOL result = [sender presentError:error];
        if (result) {
            return NSTerminateCancel;
        }

        NSString *question = NSLocalizedString(@"Could not save changes while quitting. Quit anyway?", @"Quit without saves error question message");
        NSString *info = NSLocalizedString(@"Quitting now will lose any changes you have made since the last successful save", @"Quit without saves error question info");
        NSString *quitButton = NSLocalizedString(@"Quit anyway", @"Quit anyway button title");
        NSString *cancelButton = NSLocalizedString(@"Cancel", @"Cancel button title");
        NSAlert *alert = [[NSAlert alloc] init];
        [alert setMessageText:question];
        [alert setInformativeText:info];
        [alert addButtonWithTitle:quitButton];
        [alert addButtonWithTitle:cancelButton];

        NSInteger answer = [alert runModal];

        if (answer == NSAlertFirstButtonReturn) {
            return NSTerminateCancel;
        }
    }

    return NSTerminateNow;
}

There the save: method is called, too.