Question

My app needs to be able to disconnect from a server and connect to another one at whim, which necessitates dumping whatever persistent store we have. Issue here is that releasing the ‘main’ managed object context means whatever objects in it that I have laying around fault, which causes all sorts of unexpected little issues and crashes.

Is there a better way to ‘reset’ my stack/managed objects littered around the program than just calling release on everything in my Core Data stack?

Answer 1

You need to close down you Core Data stack from the top down.

1. Make sure that no managed objects are retained by any object other than the managed object context e.g. make sure the objects aren’t held in an array owned by a UI controller.
2. Save the managed object context to clean up any loose ends.
3. Fully release the context and nil it. The context should never be retained by more than one object e.g the app delegate, anyway.
4. Send removePersistentStore:error: to the persistent store coordinator.
5. Use standard file operations to delete the actual store file.

Changing Core Data like this on the fly is difficult because Core Data isn’t just a little database hung off the side of the app. It is intended to serve as the apps entire model layer. Since Apple is really into Model-View-Controller design, then the model is the actual core of the program (hence Core Data’s name.) As such, you can’t really turn it on and off the way you would a mere SQL database.

You might actually want to rethink your design so that you can change servers without having to shut down your entire data model. E.g. simply delete all managed objects associated with an unused server.