The goal is to do insertions/changes/deletes on a background thread
and then after a save merge those changes into the main threads
managed object context and thus update the UI.
I have a situation where NSManagedObjectContextDidSaveNotification is
forwarded from a background thread's managed object context to the
main thread's managed object context (each thread has it's own managed
object context). The main thread does some processing like this (in a
subclass of NSPersistentDocument).
- (void)_mergeChangesFromContextDidSaveNotification:
(NSNotification*)notification
{
NSManagedObjectContext* __managedObjectContext = [self
managedObjectContext];
NSDate* __date = [[[NSFileManager defaultManager]
fileAttributesAtPath:[[self fileURL] path] traverseLink:YES]
objectForKey:NSFileModificationDate];
[__managedObjectContext
mergeChangesFromContextDidSaveNotification:notification];
[__managedObjectContext processPendingChanges];
[[__managedObjectContext undoManager] enableUndoRegistration];
NSLog(@"%s *1* hasChanges=%d", __FUNCTION__, [__managedObjectContext
hasChanges]);
[self setFileModificationDate:__date];
if ([__managedObjectContext hasChanges]) {
[self saveDocument:self];
}
}
- (void)mergeChangesFromContextDidSaveNotification:
(NSNotification*)notification
{
NSManagedObjectContext* __managedObjectContext = [self
managedObjectContext];
NSLog(@"%s *0* hasChanges=%d", __FUNCTION__, [__managedObjectContext
hasChanges]);
if ([__managedObjectContext hasChanges]) {
NSDate* __date = [[[NSFileManager defaultManager]
fileAttributesAtPath:[[self fileURL] path] traverseLink:YES]
objectForKey:NSFileModificationDate];
[self setFileModificationDate:__date];
[self saveDocument:self];
}
[[__managedObjectContext undoManager] disableUndoRegistration];
for (NSManagedObject* __object in [[notification userInfo]
objectForKey:NSUpdatedObjectsKey]) {
[__managedObjectContext refreshObject:[__managedObjectContext
objectWithID:[__object objectID]] mergeChanges:NO];
}
[self
performSelector
:@selector(_mergeChangesFromContextDidSaveNotification:)
withObject:notification afterDelay:0.0];
}
If I forgo the refreshObject:mergeChanges: the error doesn't occur,
but then another problem occurs where sometimes a relationship doesn't
merge correctly between 2 objects (even when there are no changes in
the main thread's managed object context the merge will sometimes
delete part of one side of the relationship. This happens with many-to-
many relationships including reflexive). By calling
refreshObject:mergeChanges: I am forcing that object to be faulted and
re-fetched with the correct data in the store.
It seems that sometimes the call to
mergeChangesFromContextDidSaveNotification: causes an error that shows
up in the output as "statement is still active". It appears that
object controllers that are bound to a managed object context receive
a notification "_NSObjectsChangedInManagingContextPrivateNotification"
and they do some fetching and the error occurs when they do a fetch
request.
I ran with the Core Data threading assertions in the _debug version of
the library and nothing special is reported.
Has anyone encountered this problem before and found a solution?
--
Michael
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