Doing something as simple as adding a new attribute to an entity in your Core Data model will break your application when it comes to opening older persistent data stores. Core Data has some support for automatic migration, documented in the “Introduction to Core Data Model Versioning and Data Migration Programming Guide” (whew!) in the Lightweight Migration section. Unfortunately, there are crucial steps that are not mentioned in this section. Kudos to Grouchal on Stack Overflow for giving us the rest of the story.
August 2, 2009