On Oct 23, 2011, at 03:13 AM, Roland King wrote:
>
> On Oct 23, 2011, at 4:18 AM, Jens Alfke wrote:
>
>>
>> On Oct 22, 2011, at 11:59 AM, Martin Hewitson wrote:
>>
>>> -migratePersistentStore:toURL:options:withType:error:
>>> Still, the core data iCloud integration remains sufficiently mysterious...
>>
>> That method’s been around since 10.4; AFAIK it just does a “save as”
>> operation to a new file. Is there some other documentation that says it
>> works specially with iCloud?
>>
>> I haven’t seen anything that implies any special treatment of CoreData
>> documents in iCloud besides just copying the entire file at once (a la
>> Dropbox.) Did I miss something that says that iCloud will sync docs at the
>> row/record/object level? If it does that, how does it handle sync conflicts,
>> partial syncs, and referential integrity?
>>
>
> Take a look at the document called 'Using Core Data with iCloud Release
> Notes' which is in the iOS5 documentation.
OK, I have read this once, but I'll read it again. I'm not working on IOS, but
I guess the core data stuff should be the same on the Mac. I'm particularly
interested in figuring out how to merge the records received when getting an
NSPersistentStoreDidImportUbiquitousContentChangesNotification.
> That gives quite a lot of information about how Core Data SQLite databases
> are supposed to work in iCloud. Indeed iCloud itself doesn't do anything much
> different with them, it continues to just keep files in sync, the difference
> here is that your Core Data SQLite store is kept locally in a directory which
> doesn't sync to iCloud, however the store is set up with an extra couple of
> keys in the persistent store options, one of which points to a log directory
> where there's a log file for each update to the database, and those do sync.
> Clearly that reduces each individual sync data usage as only one new file is
> copied. iCloud itself doesn't do anything with those, however when you open
> the store on a new device the latest logs are applied to the local database
> on that device, bringing it up to date. Similarly when you open a document
> for the first time on a new device, it creates a new local SQLite database
> and populates it.
OK, I wonder if that's what it does for a shoebox app as well?
>
> That's the theory at least. There's no discussion in that document about
> conflicts, just a small paragraph about schema changes which doesn't really
> give enough detail. Nor is there an explanation of what happens to a store
> you've been running in 'local' mode which you then move to iCloud. I don't
> believe that Core Data writes these log files for local stores and it's not
> explained how they appear when you first push the document to the cloud, as
> they would have to to to give a current snapshot of the database for new
> devices to prime the pump with.
>
> The only example I've seen is in the developer forums, in what's still called
> iOS5 Beta (and is probably thus still restricted although I hope that will
> change soon), in the iCloud section, it's sticky near the top and is called
> 'iPhoneCoreDataRecipies Sample Code'. People are definitely finding it
> frustrating and very broken at this point, especially recovery from app
> deletion on the device. My feeling from that thread is it's not quite ready
> for prime time. I took a look at Pages, Numbers and Keynote to see what they
> are doing, you can find the iCloud synced files on your mac, iCloud just
> syncs everything whether there is an application to open it or not. They use
> SQLite and what looks like Core Data however there are no logfiles and a bit
> of testing showed they just sync the whole SQLite file for each document (all
> 300K of it) every time. (I did wonder whether Apple would approve an app
> submitted by a developer which did that!).
>
> I see nowhere that SQLite is mandated, in fact the documentation talks about
> atomic stores and there are hooks in UIManagedDocument for creating them.
> UIManagedDocument out of the box does try to use SQLite and does supposedly
> set it up using the 'logfile' method, but I haven't tried it. iCloud
> integration currently only works on the device, not the sim, and I figured it
> would be quite frustrating to have to work through a new technology with
> scant documentation on the device.
>
> And finally I haven't seen a similar document in the Lion documentation. The
> keys which specify the logfile directories in the persistent store options
> exist so I've been assuming the underlying code is there, if anyone knows of
> a Lion document SQLite Core Data and Lion I'd love to read it. For iOS it
> seems fairly clear that if you use UIDocument and preferably
> UIManagedDocument your app is going to be quite iCloud friendly. On Lion,
> NSDocument seems to be the way to go but I've not yet seen an equivalent of
> the UIManagedDocument.
>
Thanks for all the information. It seems we are quite a way from routine iCloud
integration.
Martin
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Martin Hewitson
Albert-Einstein-Institut
Max-Planck-Institut fuer
Gravitationsphysik und Universitaet Hannover
Callinstr. 38, 30167 Hannover, Germany
Tel: +49-511-762-17121, Fax: +49-511-762-5861
E-Mail: [email protected]
WWW: http://www.aei.mpg.de/~hewitson
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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