How Does It Work?
The basic secret behind this new feature of Core Data is with versioning of your data model. The beautiful part of this secret is that you do not have to plan for it or deal with it in any way. Core Data keeps track of the versioning for you so that you do not have to.
All you need to do is to create a mapping model that explains to Core Data how to migrate your data from the old version to the new version. The Core Data framework takes it from there.