title: Core Data migration problem: "Persistent store migration failed, missing source managed object model."
body: <p><strong>The Background</strong></p>
  
  <ul>
  <li>A Cocoa Non Document Core Data
  project with two Managed Object
  Models. </li>
  <li>Model 1 stays the same. Model
  2 has changed, so I want to migrate
  the store.</li>
  <li>I've created a new version
  by Design > Data Model > Add Model
  Version in Xcode. </li>
  <li>The difference between versions is a single relationship that's been changed from to a one to many.</li>
  <li>I've made my
  changes to the model, then saved.</li>
  <li>I've made a new Mapping Model that
  has the old model as a source and new
  model as a destination. </li>
  <li>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. </li>
  <li>I've switched on migrations by
  passing in a dictionary with the 
  <code>NSMigratePersistentStoresAutomaticallyOption</code>
  key as <code>[NSNumber
  numberWithBool:YES]</code> when adding the
  Persistent Store. </li>
  <li>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 <code>modelByMergingModels:</code> </li>
  </ul>
  
  <p><strong>The Problem</strong></p>
  
  <p>No matter what I do to migrate, I get the error message:</p>
  
  <blockquote>
    <p>"Persistent store migration failed,
    missing source managed object model."</p>
  </blockquote>
  
  <p><strong>What I've Tried</strong></p>
  
  <ul>
  <li>I clean after every single build.</li>
  <li>I've tried various combinations of
  having only the model I'm migrating
  to in Resources, being compiled, or
  both.  </li>
  <li>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. </li>
  <li>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.</li>
  <li>I've deleted the Mapping
  Model and the new version of the
  model, cleaned, then recreated both.</li>
  <li>I've tried making a different change
  in the new model - deleting an entity
  instead.</li>
  </ul>
  
  <p><strong>I'm at my wits end.</strong></p>
  
  <p>I can't help but think I've made a huge mistake somewhere that I'm not seeing. Any ideas?</p>