Question

The Background

• A Cocoa Non Document Core Data
  project with two Managed Object
  Models.
• Model 1 stays the same. Model
  2 has changed, so I want to migrate
  the store.
• I’ve created a new version
  by Design > Data Model > Add Model
  Version in Xcode.
• The difference between versions is a single relationship that’s been changed from to a one to many.
• I’ve made my
  changes to the model, then saved.
• I’ve made a new Mapping Model that
  has the old model as a source and new
  model as a destination.
• I’ve ensured
  all Mapping Models and Data Models
  and are being compiled and all are
  copied to the Resource folder of my
  app bundle.
• I’ve switched on migrations by
  passing in a dictionary with the
  NSMigratePersistentStoresAutomaticallyOption
  key as [NSNumber
numberWithBool:YES] when adding the
  Persistent Store.
• Rather than merging
  all models in the bundle, I’ve specified the two
  models I want to use (model 1 and the
  new version of model 2) and merged
  them using modelByMergingModels:

The Problem

No matter what I do to migrate, I get the error message:

“Persistent store migration failed,
missing source managed object model.”

What I’ve Tried

• I clean after every single build.
• I’ve tried various combinations of
  having only the model I’m migrating
  to in Resources, being compiled, or
  both.
• Since the error message
  implies it can’t find the source
  model for my migration, I’ve tried
  having every version of the model in
  both the Resources folder and being
  compiled.
• I’ve made sure I’m not
  making a really basic error by
  switching back to the original
  version of my data model. The app
  runs fine.
• I’ve deleted the Mapping
  Model and the new version of the
  model, cleaned, then recreated both.
• I’ve tried making a different change
  in the new model – deleting an entity
  instead.

I’m at my wits end.

I can’t help but think I’ve made a huge mistake somewhere that I’m not seeing. Any ideas?

Answer 1

Two possibilities:

1. Your source model in your app does not match the actual store on disk.
2. Your mapping model does not match your source model.

Turn on Core Data debugging and you should be able to see the hashes that Core Data is looking for when it is doing the migration. Compare these hashes to what is in your store on disk and see if they match up. Likewise the debugging should let you see the hashes in the mapping model to help you match everything up.

If it is just your mapping model that is misaligned, you can tell it to update from source from the design menu in Xcode. If you are missing the actual source model for your store file on disk then you can look in your version control system or try using an automatic migration to get that file to migrate to the model that you believe is the source.

Update 1

The location for changing the source and destination models has moved to the bottom of the editor window: