RubyMotion でシンプルな CoreData のマイグレーションを行うコード

migrate_one_to_two.rb

module MigrateOneToTwo
  module_function

  def store_path
    File.join(App.documents_path, 'store.sqlite')
  end

  def tmp_store_path
    File.join(App.documents_path, 'store_tmp.sqlite')
  end

  def migrate_needed?
    return false unless FileTest.exist?(store_path)
    error_ptr = Pointer.new(:object)
    meta = NSPersistentStoreCoordinator.metadataForPersistentStoreOfType(NSSQLiteStoreType, URL:NSURL.fileURLWithPath(store_path), error:error_ptr)
    error = error_ptr[0]
    if error
      log_error error
      return false
    end
    ver = meta["NSStoreModelVersionIdentifiers"][0]
    ver == '' || ver == 'ver1'
  end

  def migrate!
    migrate_store(
      NSURL.fileURLWithPath(store_path),
      NSURL.fileURLWithPath(tmp_store_path)
    )
  end

  def migrate_store(store_url, dst_store_url)
    source_model = model('DataModel.mom')
    dst_model    = model('DataModel 2.mom')

    error_ptr = Pointer.new(:object)
    mapping_model = NSMappingModel.inferredMappingModelForSourceModel(source_model, destinationModel:dst_model, error:error_ptr)
    error = error_ptr[0]
    log_error error unless error.nil?
    return false if mapping_model.nil?

    manager = NSMigrationManager.alloc.initWithSourceModel(source_model, destinationModel:dst_model)
    result = manager.migrateStoreFromURL(store_url, type:NSSQLiteStoreType, options:nil, withMappingModel:mapping_model, toDestinationURL:dst_store_url, destinationType:NSSQLiteStoreType, destinationOptions:nil, error:error_ptr)
    error = error_ptr[0]
    log_error error unless error.nil?

    if result
      # リネームして上書き
      error_ptr = Pointer.new(:object)
      manager = NSFileManager.defaultManager

      manager.removeItemAtPath(store_path, error:error_ptr)
      error = error_ptr[0]
      unless error.nil?
        log_error error
        return false
      end

      manager.moveItemAtPath(tmp_store_path, toPath:store_path, error:error_ptr)
      error = error_ptr[0]
      unless error.nil?
        log_error error
        return false
      end
    end

    return result
  end

  def model(model_name)
    url = NSURL.fileURLWithPath(
        File.join(App.resources_path, 'DataModel.momd', model_name))
    NSManagedObjectModel.alloc.initWithContentsOfURL(url)
  end
end

NSStoreModelVersionIdentifiers は ver1, ver2, ver3...みたいに入力することにしたが、既に配布済みのver1にはそれを入れていないため、migrate_needed?の最後の行のようになっている。