Core Data: Inverse relationship only mirrors when I edit the mutableset. Not sure why.

Question

My model is setup so Business has many clients, Client has one business. Inverse relationship is setup in the mom file.

I have a unit test like this:

- (void)testNewClientFromBusiness
{
    PTBusiness *business = [modelController newBusiness];
    STAssertTrue([[business clients] count] == 0, @"is actually %d", [[business clients] count]);
    PTClient *client = [business newClient];
    STAssertTrue([business isEqual:[client business]], nil);
    STAssertTrue([[business clients] count] == 1, @"is actually %d", [[business clients] count]);
}

I implement -newClient inside of PTBusiness like this:

- (PTClient *)newClient
{
    PTClient *client = [NSEntityDescription insertNewObjectForEntityForName:@"Client" inManagedObjectContext:[self managedObjectContext]];
    [client setBusiness:self];
    [client updateLocalDefaultsBasedOnBusiness];
    return client;
}

The test fails because [[business clients] count] is still 0 after -newClient is called.

If I impliment it like this:

- (PTClient *)newClient
{
    PTClient *client = [NSEntityDescription insertNewObjectForEntityForName:@"Client" inManagedObjectContext:[self managedObjectContext]];
    NSMutableSet *group = [self mutableSetValueForKey:@"clients"];
    [group addObject:client];
    [client updateLocalDefaultsBasedOnBusiness];
    return client;
}

The tests passes.

My question(s): So am I right in thinking the inverse relationship is only updated when I interact with the mutable set? That seems to go against some other Core Data docs I've read. Is the fact that this is running in a unit test without a run loop have anything to do with it?

Any other troubleshooting recommendations? I'd really like to figure out why I can't set up the relationship at the client end.

Update: Some people have suggested I use -processPendingChanges to for the relationships be updated before the end of the run loop where it typically happens. Doing this is not helping me. Another sample test that fails:

- (void)testAssigningRelationship
{
    // BUG: for some unknow reason in this project i have to assign both ends of the relationsip manually.
    NSURL *modelUrl = [NSURL fileURLWithPath:[NSString stringWithFormat:@"%@/%@", [[NSBundle mainBundle] resourcePath], @"PTDataModel.momd/schemaVersion1.mom"]];
    NSManagedObjectModel *managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelUrl]; 

    NSPersistentStoreCoordinator *persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:managedObjectModel];
    [persistentStoreCoordinator addPersistentStoreWithType:NSInMemoryStoreType configuration:nil URL:nil options:nil error:nil];

    NSManagedObjectContext *managedObjectContext = [[NSManagedObjectContext alloc] init];
    [managedObjectContext setPersistentStoreCoordinator:persistentStoreCoordinator];

    PTBusiness *business = [NSEntityDescription insertNewObjectForEntityForName:@"Business" inManagedObjectContext:managedObjectContext];
    STAssertTrue([[business clients] count] == 0, @"is actually %d", [[business clients] count]);
    PTClient *client = [NSEntityDescription insertNewObjectForEntityForName:@"Client" inManagedObjectContext:managedObjectContext];
    //NSMutableSet *clients = [business valueForKey:@"clients"];
    //[clients addObject:client];
    [client setBusiness:business];
    [managedObjectContext processPendingChanges];
    STAssertTrue([business isEqual:[client business]], @"[client business] is %@", [client business]);
    // fails count is 0
            STAssertTrue([[business clients] count] == 1, @"is actually %d", [[business clients] count]);
    NSSet *clientSet = [business valueForKey:@"clients"];
    // fails count is 0
            STAssertTrue([clientSet count] == 1, @"is actually %d", [clientSet count]);
}

I've tried to recreate the bug in a fresh project that mirrors my own project's core data stack, but the fresh projects seem to work correctly. I'm really at a lose where to troubleshoot next. Sure I can work around this is my code (always use the mutableSet) but I worry about this being the tip of a bigger problem.

Answer 1

Inverse relationships are only handled at the end of the runloop typically. You can force it to happen earlier though by calling -processPendingChanges on your context.

Also, in your second example using the mutableSetValueForKey: you should have the inverse problem because there your PTClient object's business relationship would be nil.

Answer 2

Thanks for all your help people but the lack of updated inverse relationships seems to have been caused by a very subtle KCV bug in that inside of PTClient I had a relationship called business and a method (for compatibility with a previous implementation) called -isBusiness.

More info and a sample project demo-ing the bug is on my blog:

http://blog.clickablebliss.com/2010/04/09/walkthrough-of-a-recent-core-data-bug/

Thanks again.