Changes saved from one NSManagedObjectContext doesn't reflect on main NSManagedObjectContext - objective-c

Question

I have a main NSManagedObjectContext that's created in the appDelegate.
Now, I'm using another NSManagedObjectContext for editing/adding new objects without affecting the main NSManagedObjectContext, until I save them.
When I save the second NSManagedObjectContext, the changes are not reflected in the main NSManagedObjectContext, yet if I open the .sqlite database from simulator, the changes have been saved correctly into the .sqlite database. It doesn't matter if I fetch the data again, or even if I create a third NSManagedObjectContext, I cannot see those changes from the second NSManagedObjectContext, despite the fact those changes do actually exist on disk at this point.
If I quit and re-open the app, all changes are there.
What can cause the main NSManagedObjectContext to not see the new changes present in the persistent store?
Before this approach, I was using a single NSManagedObjectContext and undoManager, but I wanted to change it to use two different NSManagedObjectContexts.
The second NSManagedObjectContext save:
NSError* error = nil;
if ([managedObjectContext hasChanges]) {
NSLog(#"This new object has changes");
}
if (![managedObjectContext save:&error]) {
NSLog(#"Failed to save to data store: %#", [error localizedDescription]);
NSArray* detailedErrors = [[error userInfo] objectForKey:NSDetailedErrorsKey];
if(detailedErrors != nil && [detailedErrors count] > 0) {
for(NSError* detailedError in detailedErrors) {
NSLog(#" DetailedError: %#", [detailedError userInfo]);
}
}
else {
NSLog(#" %#", [error userInfo]);
}
}

Answer 1

If you haven't already done so, I suggest reading the Apple documentation on Core Data : Change Management.
You need to notify the first context of the changes that were saved through the second context. When saving a context, it posts a NSManagedObjectContextDidSaveNotification. Register for that notification. In the handler method, merge into the first context the changes saved through the second context. For example:
// second managed object context save
// register for the notification
[[NSNotificationCenter defaultCenter]
addObserver:self
selector:#selector(handleDidSaveNotification:)
name:NSManagedObjectContextDidSaveNotification
object:secondManagedObjectContext];
// rest of the code ommitted for clarity
if (![secondManagedObjectContext save:&error]) {
// ...
}
// unregister from notification
[[NSNotificationCenter defaultCenter]
removeObserver:self
name:NSManagedObjectContextDidSaveNotification
object:secondManagedObjectContext];
Notification handler:
- (void)handleDidSaveNotification:(NSNotification *)note {
[firstManagedObjectContext mergeChangesFromContextDidSaveNotification:note];
}