Core data and saving the context in subViewControllers, ok to release?

Question

When updating the managedObjectContext is it ok practice to do the save setup in view controllers that may be released or should the appDelegate handle the saving of the managedObjectContext so that even if the viewController is released the save finishes?

I'm leaning towards the idea of moving the save step into my appDelegate and having viewControllers call [appDelegate saveContext]; when an update is made, though perhaps thats moot since the viewController won't finish releasing until its done saving to CD either way...?

For instance, is there any difference between these two actions, done from a subViewController:

[appDelegate.managedObjectContext save:&error]

and

[appDlegate saveContext]

Where there is a method in appDelegate that runs [managedObjectContext save:&error]

Thanks, Sam

Answer 1

If you're just using one managedObjectContext through your app, it's not a bad idea to keep the save functionality in the app delegate, so that regardless of the state of your view controllers through the application's lifecycle, any updates will be saved when the app terminates.

That being said, I've found it useful to add additional save points, sometimes in view controllers, that will save the database after doing some significant updates. This way I've got my data saved even if the app crashes or the final save operation is otherwise prevented from completing.

I'm a relative newbie to Core Data so please inform me if this is bad practice.

Answer 2

Guessing that your application is single threaded, you are guaranteed that the save will finish before the view controller is released because the thread will block on the save.

If you are running a multi-threaded application; then

1. You should not be saving on the background thread, that is dangerous in Core Data.

2. You should not be accessing the view controller on the background thread because all view related activity should be performed on the main thread.

Therefore, there is no "correct" situation where you would have to worry about a -save: not finishing no matter what object you call it from because it is a blocking call.