Shows how to merge a NSManagedObjectContextDidSaveNotification from a different PSC

CoreData.m

/* When adding the persistent store to a PSC

pragmaOptions = [[NSDictionary alloc] initWithObjectsAndKeys:@"WAL", @"journal_mode", nil];
storeOptions = [[NSDictionary alloc] initWithObjectsAndKeys:pragmaOptions, NSSQLitePragmasOption, nil];

This will allow multiple readers, and at most writer to connect to the Sqlite DB.  Default journalling only allows multiple readers OR 1 writer (ie. writing blocks all reading).

*/

- (NSSet *)convertObjects:(NSSet *)objects toContext:(NSManagedObjectContext *)context {
	NSCParameterAssert([context persistentStoreCoordinator] != nil);
	NSMutableSet *mutableObjects = [NSMutableSet setWithCapacity:[objects count]];
	[objects enumerateObjectsUsingBlock:^(NSManagedObject* obj, BOOL *stop) {
		NSURL *objectURI = [[obj objectID] URIRepresentation];
		NSManagedObjectID *objectID = [[context persistentStoreCoordinator] managedObjectIDForURIRepresentation:objectURI];
		NSManagedObject *object = [context objectWithID:objectID];
		[mutableObjects addObject:object];
	}];
	return mutableObjects;
}

- (void)mergeChangesFromRootContext:(NSNotification*)note {
	if ([note object] == [self rootContext]) {
		NSManagedObjectContext *mainContext = [self mainContext];
		[mainContext performBlock:^{
			NSDictionary *userInfo = [note userInfo];

			NSSet *insertedObjects = [self convertObjects:[userInfo objectForKey:NSInsertedObjectsKey] toContext:mainContext];
			NSSet *deletedObjects = [self convertObjects:[userInfo objectForKey:NSDeletedObjectsKey] toContext:mainContext];
			NSSet *updatedObjects = [self convertObjects:[userInfo objectForKey:NSUpdatedObjectsKey] toContext:mainContext];

			NSDictionary *newUserInfo = @{ NSInsertedObjectsKey: insertedObjects, NSDeletedObjectsKey: deletedObjects, NSUpdatedObjectsKey : updatedObjects };

			NSNotification *localNotification = [NSNotification notificationWithName:NSManagedObjectContextDidSaveNotification object:[self rootContext] userInfo:newUserInfo];
			
			[[self mainContext] mergeChangesFromContextDidSaveNotification:localNotification];
		}];
	}
}