title: I keep on getting "save operation failure" after any change on my Xcode Data Model
body: <p>I started using Core Data for iPhone development. I started out by creating a very simple entity (called Evaluation) with just one string property (called evaluationTopic). I had following code for inserting a fresh string:</p>
  
  <pre><code>- (void)insertNewObject {
  
      // Create a new instance of the entity managed by the fetched results controller.
      NSManagedObjectContext *context = [fetchedResultsController managedObjectContext];
      NSEntityDescription *entity = [[fetchedResultsController fetchRequest] entity];
      NSManagedObject *newManagedObject = [NSEntityDescription insertNewObjectForEntityForName:[entity name] inManagedObjectContext:context];
  
      // If appropriate, configure the new managed object.
      [newManagedObject setValue:@"My Repeating String" forKey:@"evaluationTopic"];
  
      // Save the context.
      NSError *error;
      if (![context save:&amp;error]) {
          // Handle the error...
      }
  
      [self.tableView reloadData];
  }
  </code></pre>
  
  <p>This worked perfectly fine and by pushing the +button a new "My Repeating String" would be added to the table view and be in persistent store.</p>
  
  <p>I then pressed "Design -> Add Model Version" in Xcode. I added three entities to the existing entity and also added new properties to the existing "Evaluation" entity. Then, I created new files off the entities by pressing "File -> New File -> Managed Object Classes" and created a new .h and .m file for my four entities, including the "Evaluation" entity with Evaluation.h and Evaluation.m. Now I changed the model version by setting "Design -> Data Model -> Set Current Version". After having done all this, I changed my insertMethod:</p>
  
  <pre><code>- (void)insertNewObject {
  
      // Create a new instance of the entity managed by the fetched results controller.
      NSManagedObjectContext *context = [fetchedResultsController managedObjectContext];
      NSEntityDescription *entity = [[fetchedResultsController fetchRequest] entity];
      Evaluation *evaluation = (Evaluation *) [NSEntityDescription insertNewObjectForEntityForName:[entity name] inManagedObjectContext:context];
  
      // If appropriate, configure the new managed object.
      [evaluation setValue:@"My even new string" forKey:@"evaluationSpeechTopic"];
  
      // Save the context.
      NSError *error;
      if (![context save:&amp;error]) {
          // Handle the error...
      }
  
      [self.tableView reloadData];
  }
  </code></pre>
  
  <p>This does not work though! Every time I want to add a row the simulator crashes and I get the following:</p>
  
  <pre><code>"NSInternalInconsistencyException', reason: 'This NSPersistentStoreCoordinator has no persistent stores.  It cannot perform a save operation.'"
  </code></pre>
  
  <p>I had this error before I knew about creating new version after changing anything on the datamodel, but why is this still coming up? Do I need to do any mapping (even though I just added entities and properties that did not exist before?). In the Apple Dev tutorial it sounds very easy but I have been struggling with this for long time, never worked after changing model version.</p>