Two Contexts, 1 Persistent Store: Duplicate Fetched Entries - iphone

Question

I am attempting to create a way for users to import contacts to their phone. How it works is this:
There are two managed object contexts. The "real" context has the current data in their address book. The "other" context has incoming data from another source. Both share the same PersistentStoreCoordinator.
I match people by e-mail, so if a contact in the "real" context matches one in the "other", I don't save the other.
When I start the program, I have two entries in the "real" context that I can fetch fine.
Then, I import two other contacts an add them to the "other" context.
When I perform a fetch operation on the "other" context, I get FOUR results - two from the "real" context and two I just added to the "other" context.
However, when I merge the changes, my scheme for detecting duplicates works.
Is there something I'm missing with my understanding of Core Data? How can I make it so that my querying of the "other" context just returns the new results.
The full code is really long, but here's the important part:
AppDelegate *appDel = (AppDelegate*)[[UIApplication sharedApplication] delegate];
// Check to see the original data
NSManagedObjectContext *realContext = [appDel managedObjectContext];
NSFetchRequest *usersFetch= [[[NSFetchRequest alloc] init] autorelease];
[usersFetch setEntity:[NSEntityDescription entityForName:#"User" inManagedObjectContext:realContext]];
[usersFetch setSortDescriptors:[NSArray arrayWithObject:[NSSortDescriptor sortDescriptorWithKey:#"email" ascending:YES]]];
NSArray *users = [realContext executeFetchRequest:usersFetch error:&error];
[usersFetch release];
NSLog(#"%#",users); // Returns 2 original objects already in database
otherContext = [[NSManagedObjectContext alloc] init];
[otherContext setPersistentStoreCoordinator:[[appDel managedObjectContext] persistentStoreCoordinator]];
for (contacts in fetchedData){
User *newUser = (User*)[NSEntityDescription insertNewObjectForEntityForName:#"User" inManagedObjectContext:otherContext];
newUser.email = fetchedData.email;
newUser.firstName = fetchedData.firstName;
// etc.
}
NSFetchRequest *newUsersFetch = [[[NSFetchRequest alloc] init] autorelease];
[newUsersFetch setEntity:[NSEntityDescription entityForName:#"User" inManagedObjectContext:otherContext]];
[newUsersFetch setSortDescriptors:[NSArray arrayWithObject:[NSSortDescriptor sortDescriptorWithKey:#"email" ascending:YES]]];
NSLog(#"%#",[otherContext registeredObjects]); // 2 objects that were just added
NSArray *newUsers = [otherContext executeFetchRequest:newUsersFetch error:&error];
NSLog(#"%#",[otherContext registeredObjects]); // 4 objects - added AND original
NSLog(#"Count: %i",[newUsers count]); // Count: 4

Answer 1

I think you may be conceptually confusing the managed object contexts with the persistent store. You can have an arbitrary number of context attached to a particular store and the changes made in any single context will eventually show up in all the others.
This is especially true of fetches which go directly to the store to find objects. Your code is working as expected if you call a save on the other context. Once you save an object, it goes into the persistent store and will show up in all entity wide fetches.
You should not be creating managed objects that might have duplicates. Instead, the normal practice is to fetch on new values to see if they already exist and only create a new managed object with the value if the value does not already exist in the store. To make that fast, you can do a fetch for a specific property and see if anything is returned.