But if you’re writing your model in code, you probably don’t want to, because that’s even deeper magic than the model editor. As with the model, you can do it all in code, but as with code, it means working in some rarely used corners of the Core Data framework. The details are more than I’m going to get into here, but whatever you do, keep the code for the old model because you’ll need both old and new data models to do the migration.