-(BOOL)loadObjectModels:(NSString*)modelName {
 
  NSString* momdPath = [[NSBundle mainBundle] pathForResource:modelName ofType:@"momd"];
  NSBundle* modelBundle = [NSBundle bundleWithPath:momdPath];
  NSString* plistPath = [modelBundle pathForResource:@"VersionInfo" ofType:@"plist"];
  NSData* plistData = [NSData dataWithContentsOfFile:plistPath];
  NSString *error;
 
  NSDictionary* versionInfo = [NSPropertyListSerialization propertyListFromData:plistData 
                                                 mutabilityOption:NSPropertyListImmutable
                                                           format:NULL
                                                 errorDescription:&error];
  if ( error ) {
    NSLog(@"An error occurred retrieving versionInfo --> %@", error);
    return NO;
  }
 
  NSDictionary* versionDict = [versionInfo valueForKey:@"NSManagedObjectModel_VersionHashes"];
 
  objectModels = [[NSMutableArray alloc] initWithCapacity:[versionDict count]];
  NSArray* sortedMomList = [[versionDict allKeys] sortedArrayUsingFunction:nameSort context:NULL];
 
  for (NSString* modelName in sortedMomList) {
    NSString* modelPath = [modelBundle pathForResource:modelName ofType:@"mom"];
    NSManagedObjectModel* model = 
         [[NSManagedObjectModel alloc] initWithContentsOfURL: [NSURL fileURLWithPath: modelPath]];
    [objectModels addObject:model];
    [model release];
  }
 
  return YES;
}

-(BOOL)determineModelVersion {  
  NSError* error;
  NSDictionary *storeMetadata = [NSPersistentStoreCoordinator 
                                 metadataForPersistentStoreWithURL:storeURL 
                                 error:&error];  
  if ( ! storeMetadata ) {
    return NO;
  }
 
  for( NSManagedObjectModel* model in objectModels ) {
    if ([model isConfiguration:nil compatibleWithStoreMetadata:storeMetadata] ) {
      currentStoreModel = [objectModels indexOfObject:model];
      return YES;
    }
  }
 
  return NO;
}

- (BOOL)migrationNeeded {
  return ! ( currentStoreModel == [objectModels count] );
}
 
- (BOOL)migrateIfNeeded:(NSError**)error {
 
  if ( ! [self migrationNeeded] ) {
    return YES; }
 
  // Backup the store before we do anything
  NSString* backupFilePath = [[storeURL path] stringByAppendingString:@".backup"];
  if( ![self overWriteCopy:[storeURL path] to:backupFilePath error:error] ) {
    return NO;
  }
 
  NSDictionary *opts =
  [NSDictionary dictionaryWithObject:[NSNumber numberWithBool:YES]
                              forKey:NSMigratePersistentStoresAutomaticallyOption];  
  NSInteger i;   
  NSURL* tempURL = [NSURL fileURLWithPath:[[storeURL path] stringByAppendingString:@".temp"]];
 
  for( i = currentStoreModel; i < [objectModels count] - 1; i++ ) {    
    // Migrate the store to a temp file.   
    // SunFlower.xml --> SunFlower.xml.temp
    BOOL migrationSuccess = [[self migrationManagerForIndex:i]                   
                               migrateStoreFromURL:storeURL type:NSXMLStoreType options:opts 
                               withMappingModel:[self mappingModelForIndex:i] 
                               toDestinationURL:tempURL 
                              destinationType:NSXMLStoreType destinationOptions:opts 
                               error:error];            
 
    // Revert and return if:
    // 1.) The migration failed.
    // 2.) The temp file could not be copied over the original.
    // 3.) The temp file could not be deleted.
    if (! migrationSuccess || 
        ! [self overWriteCopy:[tempURL path] to:[storeURL path] error:error] ||        
        ! [[NSFileManager defaultManager]  removeItemAtPath:[tempURL path] error:error]) {
      // Revert to backup file and exit
      // Not passing an error because we want to propogate the previous error.    
      [self overWriteCopy:backupFilePath to:[storeURL path]  error:NULL];
      return NO;
    }    
  }
 
  return YES;
}