Core Data Deletion rules and many-to-many relationships

Question

Say you have departments and employees and each department has several employees, but each employee can also be part of several departments.

So there is a many-to-ma

Answer 1

Thanks, alex. I will probably do that. In the meantime I had found a different way of doing this:

1.) register for notifications on changes:

    [[NSNotificationCenter defaultCenter] addObserver:self 
            selector:@selector(managedObjectContextDidChange:) 
            name:NSManagedObjectContextObjectsDidChangeNotification 
            object:managedObjectContext];

2.) when changes occur and an employee gets updated. I check if that object has 0 relations to departments and delete it:

- (void)managedObjectContextDidChange:(NSNotification *)notification {
    NSSet *updatedObjects = [[notification userInfo] objectForKey:NSUpdatedObjectsKey];

for(NSManagedObject *obj in updatedObjects){        
    // walk through updated objects -> check for employees
    // check if they still contain departments and if not delete them
    if([obj.entity.name isEqualToString:@"Employee"]){
        NSLog(@"Employee changed!");
        if([[(Employee*)obj Departments] count]==0){
            NSLog(@"No more relations -> Delete Employee");
            [managedObjectContext deleteObject:obj];
        }
    }
}}

That works well too, but might get more complicated if you have several different entities for which to observe this kind of behavior.