On 2009 Nov 19, at 14:05, Matthew Lindfield Seager wrote:
> I can't help with your question but Googling
> "NSMigratePersistentStoresAutomaticallyOption site:lists.apple.com"
> yields 36 results. There's probably several duplicates but it give you
> a head start
Hmmm. When I tried that this morning I only got 19. Among the additional 17,
I found this:
http://lists.apple.com/archives/cocoa-dev/2008/Aug/msg00767.html
Summary: There is no need to muck with NSPersistentDocument's built-in and
bug-free Persistence Stack. Happy Day! All you do is override
-[NSPersistentDocument initWithContentsOfURL:ofType:error:]. I submitted
document feedback suggesting this to the Core Data Model Versioning and Data
Migration Programming Guide.
Thanks, Matthew.
The code in that post had issues and didn't quite work, so I fixed it up and it
now seems to "just work" now for all three cases (1) oldest docs saved with old
model (2) old docs with new model (3) new docs. In case (1) the old file
remains with a tilde suffix, as expected. In case (3), the method doesn't even
run. But when it does, it handles errors properly :)
So, the answer to the question: How to enable Default Automatic Migration in a
Core Data document-based app, is...
Simply drop the following override into the NSPersistentDocument subclass:
- (id)initWithContentsOfURL:(NSURL*)url
ofType:(NSString*)typeName
error:(NSError**)error_p {
// NSPersistentDocument's built-in Persistence Stack seems to create a store
// without setting the NSMigratePersistentStoresAutomaticallyOption, so
// automatic migration just "doesn't work". The following code, which runs
// only for existing documents, works around that problem.
NSError* error = nil ;
NSArray* bundles = [NSArray arrayWithObject:[NSBundle mainBundle]] ;
NSManagedObjectModel* mergedMOM = [NSManagedObjectModel
mergedModelFromBundles:bundles] ;
NSPersistentStoreCoordinator *psc = [[NSPersistentStoreCoordinator alloc]
initWithManagedObjectModel:mergedMOM];
NSDictionary *optionsDictionary =
[NSDictionary dictionaryWithObject:[NSNumber numberWithBool:YES]
forKey:NSMigratePersistentStoresAutomaticallyOption];
id store = [psc addPersistentStoreWithType:NSSQLiteStoreType
configuration:nil
URL:url
options:optionsDictionary
error:&error] ;
// If migrating the document from and older to the current model was
necessary,
// it is now all done! The addPersistentStoreWithType: will have
renamed the
// old file with a tilde on the end and created a new, migrated file at the
given
// URL. So now, when we invoke super, it will open the new file and just
work.
// Very nice.
if (store) {
self = [super initWithContentsOfURL:url
ofType:typeName
error:&error] ;
// The above method will return nil if it fails.
}
else {
[self release] ;
self = nil ;
}
if (!self && error_p) {
*error_p = error ;
}
return self;
}
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