Inverse Relationship with Core Data Causes Crash when Adding Object to NSSet

Question

I have 2 entities in Core Data, a Bill and Person . I have two relationships:

• Bill to Person is a 'To Many' relationship called 'people'
• The inverse - from Person to Bill is 'To One'- called 'bill'.

The result generated by Xcode (along with the classes) are:

Bill :

extension Bill {
    @NSManaged var people: NSSet?
}

Person :

extension Person {
    @NSManaged var bill: Bill?
}

This is the method I've written to add a Person object to the Bill 's NSSet :

class Bill : NSManagedObject {
...

func addPersonToBill(contact : CNContact){

        let entDesc = NSEntityDescription.entityForName("Person", inManagedObjectContext: managedObjectContext())

// Create Person object with custom initialiser
        let person = Person(contact: contact, entity: entDesc!, insertIntoManagedObjectContext: managedObjectContext())
        print("Got person")

        people = people?.setByAddingObject(person) // CRASHES HERE
    }
}

The custom initialiser for Person is:

init(contact : CNContact, entity : NSEntityDescription, insertIntoManagedObjectContext context : NSManagedObjectContext?){
        super.init(entity: entity, insertIntoManagedObjectContext: context)
   // I set other properties here using info from the CNContact
    }

However, when I add a Person , it crashes at people?.setByAddingObject(person) with the error:

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[_TtCs21_SwiftDeferredNSArray isEqualToSet:]: unrecognized selector sent to instance 0x7fc7ed875cb0'

When I delete the bill relationship from Person to Bill , it runs fine and the Person is added to the Bill 's 'people' NSSet . I could leave it like this as I don't necessarily need this inverse relationship, but I've read that it is best to have an inverse relationship unless I have a good reason not to. I also face this issue with other relationships in my app, so I would have a lot of relationships without their inverse.

Any ideas what's wrong? Are my relationships incorrect? One Bill can have many Person s, but one Person can only have one Bill .

The solutions I've tried are:

• Adding this accessor from this answer :

  @NSManaged func addPeopleObject(value:Person)

But I get the error:

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[NSSet intersectsSet:]: set argument is not an NSSet'

• Creating an NSMutableOrderedSet as suggested by other answers:

let mutPeople = NSMutableOrderedSet(array: (people?.allObjects)!) mutOwers.addObject(person) people = NSSet(array:mutPeople.array)

...but I get the same, original crash message.

• Unwrapping 'people' - still get the same crash message.

Any help would be much appreciated, thanks.

Answer 1

Ah, I had a similar problem as [this question]. 1 I had a method on Bill called getOwers which had a return type of an array, and this seemed to override the accessor CoreData creates. I changed the method to getOwersArr , and all is fine now. Thanks to @Paulw11 for pointing me in the right direction!

Answer 2

I also have to-many relationships implemented as NSSet . I add/delete objects to the set (without any problems) using code like the following:

let mutableSet = bill.mutableSetValueForKey("people") 

mutableSet.addObject(newPerson)

// (next, save managed object context)

Answer 3

I had a similar issue with iOS 9.3 in a one-to-many relationship.

I fixed it by replacing:

group.addToTeams(team) // Crashes on iOS 9.3

with:

team.group = group // This will correctly add team to the set without crashing

Basically instead of adding and object to the set use the Inverse relationship.