Swift，Xcode 6 Beta 4：如何检索当前使用Photos框架资产显示的图像文件的文件路径？

I am currently writing an iOS app in which my intent is to save data objects associated with the app in a DB created in Core Data. I have successfully created the DB, and plan to synchronize the data objects among different devices logged in to the same iCloud-account through iCloud. In the middle of all this, I would also like media files to be associated with the distinct data objects. However, I do not wish to save the binary data constituting a media file directly to the DB. Thus I need some kind of way to preserve the reference to the correct media file in the DB. My immediate thought was to place every media file in a specific folder, turn on iCloud sync for that folder, and save the media files' filenames to the DB. However, I am not able to retrieve the file path of any media files. I am currently writing an iOS app in which my i