Question

I have a 1-to-many relationship in my example app, taken from the Core Data documentation, where one Manager has multiple employees. I get the part on how to set the Manager-to-Employee relationship delete rule, but what about the Employee-to-Manager relationship? If I want a case where, if ALL the employees have been deleted, I want the Manager to also be deleted, what kind of delete rule should I apply? Cascade doesn’t make sense, because then if one employee is deleted, the manager will get deleted even though he/she has other employees still linked. Nullify will delete the relationships correctly, but it won’t delete the Manager when the last employee has been deleted.
Am I missing something, or do I have to do something custom in this case?

Answer 1

The delete rules don’t have enough specificity to say, “delete self if relationship ‘bobs’ contains fewer than ‘x’ objects.”

Instead, you should put such business logic in a custom NSManagedObject subclass. You can put a check in the Manager classes removeEmployeeObject: and removedEmployeeObjects: method that tells the Manager instances to delete itself if the employees relationship is empty.

You can also use validation methods for this or the willSave methods.