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Plist Incremental Store

This is a demonstration app to show off an experimental NSIncrementalStore for Apple's Core Data framework. I use it for the live coding part of my NSIncrementalStore talks.

What it does

The incremental store allows Core Data to write simple models (that is, models without relationships) to Plist files in a specified directory. Not only does it read and write the entities to plist files, but it watches the directory for changes with NSFileCoordinator/NSFilePresenter. If it sees a changed or removed file, then it notifies Core Data and anyone listening for changes (like a fetched results controller) will be told of the new or removed object.

I originally built this as a research experiment to learn about Core Data and see if it would be possible to sync simple models over a filesystem. Theoretically this would work great with Dropbox (and I've done some testing with this myself). I ended up not using it on the project I was working on because I had more complex data model needs. Nonetheless, the learning experience was a remarkable success and I'm sharing what I found here in this repository.

I've commented throughout. Open an issue if something isn't clear. We can help improve this together.

How it works

The main part of the app is pretty boilerplate, just a simple Core Data Stack used by a fetched results controller to feed a table view. The interesting part starts in the PlistIncrementalStore.m file where all the magic takes place. It constructs a PlistStoreFileWatcher that acts as the sole object responsible for watching for changes and serializing access to the file system to ensure atomicity.

When this store is active, it will be notified of changes by the PlistStoreFileWatcher and tell Core Data what objects need to be handled appropriately.

So, does it work?

Yes! If you change files on disk or remove them, Core Data keeps up just fine. If you put a file that has an invalid name or contents, then the store just silently ignores them unless you have debug logging enabled.

If you tap the action button in the application, you'll see an option to create many plist files programmatically on disk in a background queue so you can watch Core Data churn through the file system notifications without breaking a sweat. It works quite well, even on an older device.


Questions? Ask!

Jonathan Penn


Schedule is available under the MIT license. See the LICENSE file for more info.


A demonstration of a custom NSIncrementalStore for Core Data







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