CoreData and iCloud; how can I track which device last saved to the cloud?

Question

I have a CoreData app (using https://github.com/lhunath/UbiquityStoreManager), backed by iCloud. In one use case a user with a local store enables iCloud (where data already exists). I want to prompt the user to make a decision of whether to migrate the local data to iCloud or just use the iCloud version. As part of this, I'd like to display the device name and last sync date of the version in iCloud.

I've been tinkering around with my NSPersistentStore's metadata, but that doesn't appear to get synced to iCloud.

Any suggestions?

Answer 1

You could use iCloud's key-value store to store the device name & date of the last sync.

Answer 2

My no doubt unpopular suggestion is "don't". Trying to determine what is in iCloud at any given time puts you on pretty shaky ground. You may be able to get it to work most of the time, but there will always be circumstances where it breaks down.

If you really must import some data when first enabling iCloud, I suggest just always importing the data, and then deduping later as the iCloud data comes in. As ugly as it sounds, that's the only approach really guaranteed to work with Apple's approach.

It is worth taking a look at other Core Data sync frameworks like TICDS and Ensembles. They take a more sane approach to data identity, which means you can avoid the whole deduping step. (Disclosure: I develop Ensembles)

Answer 3

do a metadata query on the iCloud files and check the most recent transaction log file in iCloud. See the link below for a sample app that uses this approach to check whether the app is properly synchronised with iCloud.
http://ossh.com.au/design-and-technology/software-development/sample-library-style-ios-core-data-app-with-icloud-integration/

EDIT: I just realised I don't get the actual device name, but once you have found the most recent log file then use this to get the device. Just be aware this call may be expensive.

NSFileVersion *openedVersion = [NSFileVersion currentVersionOfItemAtURL:fileURL];
    return openedVersion.localizedNameOfSavingComputer;