Recommended document structure. File Wrappers? Roll my own?

Question

Hi, I'm currently working out the best structure for a document I'm trying to create. The document is basically a core data document that uses sqlite as its store, but uses the Apple provided NSPersistentDocument+FileWrapperSupport to enable file wrapper support.

The document makes heavy use of media, such as images, videos, audio files, etc. with potentially 1000s of files. So what I'm trying to do is create a structure similar to the following:

/myfile.ext/
/myfile.ext/store.sqlite
/myfile.ext/content/
/myfile.ext/content/images/*
/myfile.ext/content/videos/*
/myfile.ext/content/audio/*

Now, first of all I went down the route of creating a temporary directory and placing all of my media in there. Basically creating the paths and file names '/content/images/image1.jpg' as I wanted them to appear in the saved file wrapper, and then upon save I attempted to copy these all into the filewrapper...

What I found was that the files were indeed copied into the wrapper with the file structure I wanted, but when the actual wrapper was saved, these files all magically disappeared.

Great.

So, I trashed my existing solution and tried to use file wrappers instead. This solution involved creating a content wrapper file directory when a new document was created, or loading in a content directory file wrapper upon opening a document.

When an image was added/modified, I created the necessary directory wrappers inside this root content wrapper (i.e. an images directory wrapper if it didn't already exist, or any other intermediary directory wrappers that needed to be created) and then created a regular file wrapper for the media, removing any existing wrapper for that file name if one was there.

Saving the document was just a case of making sure the content file wrapper was added to the document file wrapper, and the document would save.

Well... it did. The first time. However, any attempts to make any subsequent changes i.e add an image, save. Then replace image, save. Did not behave as expected, only showing the image from the first save.

So, my question is... first of all, which of the above approaches is the correct one, if at all, and what am I doing that wrong for them to fail.

And secondly, as I expect to be managing 1000s of images, is using file wrappers the correct way to go about things at all.

Answer 1

With that much media in play, you should likely give your users control over whether the media resides in the document or only a reference to the media is included in the document, and the media resides elsewhere, such as in a library/repository managed by your application. Then they could save out a (potentially many times larger) copy with all references resolved.

You might want to zip/unzip any directory so that users don't get confused trying to attach the document to an email. I believe iWork has been doing this with its document bundles for a while now.

As far as what you are doing wrong, no-one can say, as you haven't provided any code demonstrating what you are doing.

Why don't you create a one-off application that lets you select files on disk and saves those files in a document using a file wrapper? This would let you tackle this functionality without any interference from other issues in your application. Once you understand how to use file wrappers, you can port the code back or just write new code that works.