Question

I have a fairly straightforward data model for a Core Data app. Basically, I’m bringing up
a list of contacts already on the phone. When a user taps a contact, they’re taken
to a detail view screen, where they can select a phone number or email address. When they
select any detail item, I’m storing it via Core Data.

I have one entity called Contact, and another called Contact_Detail.

Contact <—–>> Contact_Detail

The Contact relationship to Contact_Detail has a delete rule of Deny.
The Contact_Detail relationship to Contact has a delete rule of No Action.

If a user wants to remove, say, a previously selected detail item, I first fetch the
Contact_Detail objects that have the same ID as the Contact. If there is only one Contact_Detail
object returned, I then know I need to remove the contact as well from the Contact entity. If there
were more than one Contact_Detail object returned, I just remove that particular object.

It’s all working fine, and the database is getting updated as expected (detail objects removed, and when the
last detail object for a particular contact is removed, so is the contact) as long as I just go back and forth
between the peoplePicker and the peopleDetailViewController.

The problem I’m having is that when I select an email address, leave the detailVC, leave the peoplePicker, then
return back to the peoplePicker, and back to the same contact, and deselect the email address I previously
selected, Core Data is throwing an error that looks as though it can’t delete my Contact because there are
still relationship objects (the Contact_Detail):

NSValidationErrorKey=details, NSLocalizedDescription=The operation couldn’t be completed. (Cocoa error 1600.), NSValidationErrorValue=Relationship objects for {(
     (entity: Contact_Detail; id: 0xd21afe0  ; data: )
)} on 0x5d5a780}

I can verify that the Contact_Detail object does in fact get removed. Why can’t the Contact be removed? And why
does this only happen with a particular sequence of navigation?

Let me know if I should post some code. I think this problem is causing a crash I’m seeing after continuing to work with Core Data after this first error is thrown.

Thanks!

Answer 1

Why don’t you set delete rules in this way?

Contact<--(cascade)-->>ContactDetail
//when Contact is removed, all details are removed too)

ContactDetail<<--(nullify)-->Contact
//when Contact Detail is removed, this particular detail is removed from Contact too