title: Error adding NSEntity to a NSOrderedSet
body: <p>I have 2 Entities in my <code>CoreData</code> structure , there is a One-to-many relationship between them. In the Main Entity I have a NSOrderdSet, every time I make a new save I want to add and save the 2nd entity in the NSOrderdSet, but I get an Error.
   Here is my code:</p>
  
  <pre><code>//main Entity 
  class Project : NSManagedObject {
  func requestAddNewWeek (value: WeekContent) {
  let mutableCopyOfSet = projectContent?.mutableCopy() as! NSMutableOrderdSet
  mutableCopyOfSet.addObject(value)
  projectContent = mutableCopyOfSet.copy() as ? NSOderedSet
  }
  }
  
  // ViewController where the save occurs
  class SetupWeekViewController {
  var project : Project?
  
  @IBAction func saveButton (sender : AnyObject) {
   let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
  let managedContext : NSManagedObjectContext = appDelegate.managedObjectContext
   let entity = NSEntityDescription.entityForName("Content", inManagedObjectContext:managedObjectContext
  //Here is where the error happens
  project!requestAddNewWeek(newWeek)
  
  managedContext.save()
  }
  </code></pre>
  
  <p>//Here is the error I get </p>
  
  <pre><code>2015-12-08 11:07:13.392 MySightwords[1998:189666] CoreData: error: -addPersistentStoreWithType:SQLite configuration:(null) URL:file:///Users/Len/Library/Developer/CoreSimulator/Devices/0215DFE7-14EA-459F-991C-5ABF8020712D/data/Containers/Data/Application/7A509174-D568-4CCE-8A3D-9710FF80A9BF/Documents/SingleViewCoreData.sqlite options:(null) ... returned error Error Domain=NSCocoaErrorDomain Code=134100 "(null)" UserInfo={metadata={
      NSPersistenceFrameworkVersion = 640;
      NSStoreModelVersionHashes =     {
          Content = &lt;16a6b5d3 e57d053c f85d1afa 2efe7c04 8da974e7 127f2c6b 847ea2f0 b63d732f&gt;;
          Project = &lt;97588fff 696dabc6 896ec617 564b473f f3bc9bdc e6c891b3 84519149 9319c454&gt;;
          Sightwords = &lt;6bf96219 adc3369d 4eec0597 b40472c3 d3af6a61 3d17bd5d 117885f4 509ecd2e&gt;;
      };
      NSStoreModelVersionHashesVersion = 3;
      NSStoreModelVersionIdentifiers =     (
          ""
      );
      NSStoreType = SQLite;
      NSStoreUUID = "270A2DB1-BFDA-41A3-B044-DFBA717A1BDD";
      "_NSAutoVacuumLevel" = 2;
  }, reason=The model used to open the store is incompatible with the one used to create the store} with userInfo dictionary {
      metadata =     {
          NSPersistenceFrameworkVersion = 640;
          NSStoreModelVersionHashes =         {
              Content = &lt;16a6b5d3 e57d053c f85d1afa 2efe7c04 8da974e7 127f2c6b 847ea2f0 b63d732f&gt;;
              Project = &lt;97588fff 696dabc6 896ec617 564b473f f3bc9bdc e6c891b3 84519149 9319c454&gt;;
              Sightwords = &lt;6bf96219 adc3369d 4eec0597 b40472c3 d3af6a61 3d17bd5d 117885f4 509ecd2e&gt;;
          };
          NSStoreModelVersionHashesVersion = 3;
          NSStoreModelVersionIdentifiers =         (
              ""
          );
          NSStoreType = SQLite;
          NSStoreUUID = "270A2DB1-BFDA-41A3-B044-DFBA717A1BDD";
          "_NSAutoVacuumLevel" = 2;
      };
      reason = "The model used to open the store is incompatible with the one used to create the store";
  }
  2015-12-08 11:07:13.396 MySightwords[1998:189666] Unresolved error Error Domain=YOUR_ERROR_DOMAIN Code=9999 "Failed to initialize the application's saved data" UserInfo={NSLocalizedDescription=Failed to initialize the application's saved data, NSLocalizedFailureReason=There was an error creating or loading the application's saved data., NSUnderlyingError=0x7ff7025e9200 {Error Domain=NSCocoaErrorDomain Code=134100 "(null)" UserInfo={metadata={
      NSPersistenceFrameworkVersion = 640;
      NSStoreModelVersionHashes =     {
          Content = &lt;16a6b5d3 e57d053c f85d1afa 2efe7c04 8da974e7 127f2c6b 847ea2f0 b63d732f&gt;;
          Project = &lt;97588fff 696dabc6 896ec617 564b473f f3bc9bdc e6c891b3 84519149 9319c454&gt;;
          Sightwords = &lt;6bf96219 adc3369d 4eec0597 b40472c3 d3af6a61 3d17bd5d 117885f4 509ecd2e&gt;;
      };
      NSStoreModelVersionHashesVersion = 3;
      NSStoreModelVersionIdentifiers =     (
          ""
      );
      NSStoreType = SQLite;
      NSStoreUUID = "270A2DB1-BFDA-41A3-B044-DFBA717A1BDD";
      "_NSAutoVacuumLevel" = 2;
  }, reason=The model used to open the store is incompatible with the one used to create the store}}}, [NSLocalizedDescription: Failed to initialize the application's saved data, NSLocalizedFailureReason: There was an error creating or loading the application's saved data., NSUnderlyingError: Error Domain=NSCocoaErrorDomain Code=134100 "(null)" UserInfo={metadata={
      NSPersistenceFrameworkVersion = 640;
      NSStoreModelVersionHashes =     {
          Content = &lt;16a6b5d3 e57d053c f85d1afa 2efe7c04 8da974e7 127f2c6b 847ea2f0 b63d732f&gt;;
          Project = &lt;97588fff 696dabc6 896ec617 564b473f f3bc9bdc e6c891b3 84519149 9319c454&gt;;
          Sightwords = &lt;6bf96219 adc3369d 4eec0597 b40472c3 d3af6a61 3d17bd5d 117885f4 509ecd2e&gt;;
      };
      NSStoreModelVersionHashesVersion = 3;
      NSStoreModelVersionIdentifiers =     (
          ""
      );
      NSStoreType = SQLite;
      NSStoreUUID = "270A2DB1-BFDA-41A3-B044-DFBA717A1BDD";
      "_NSAutoVacuumLevel" = 2;
  }, reason=The model used to open the store is incompatible with the one used to create the store}]
  (lldb) 
  </code></pre>