Adding An Item To An NSSet For A Core Data One To Many Relationship

Question

I have a core data relationship where one entity holds many of another entity. As far as I am aware each instance of the many class is held inside an NSSet? inside the one class. (?)

My question is - what is the best way to add items to this set? I figure this must be a very common problem - but I cannot seem to find an easy method.

This is my attempt: (This is all taken from the one class)

static var timeSlotItems: NSSet? //The Set that holds the many?


...



static func saveTimeSlot(timeSlot: TimeSlot) { //TimeSlot is the many object
    retrieveValues()
    var timeSlotArray = Array(self.timeSlotItems!)
    timeSlotArray.append(timeSlot)
    var setTimeSlotItems = Set(timeSlotArray)
    self.timeSlotItems = setTimeSlotItems // This is the error line

}

Where retrieveValues() just updates all the coreData values in the class. TimeSlot is the many object which I want to add.

I get an error on the last line, the error is: "cannot invoke initializer for type Set<_> with an argument of list of type Array"

Am I conceptually wrong at all? Thanks!

Answer 1

For one-to-many this is easy. Just use the reverse to-one relationship.

timeSlot.item = self

For many-to-many I use this convenience method:

// Support adding to many-to-many relationships

extension NSManagedObject {
    func addObject(value: NSManagedObject, forKey key: String) {
        let items = self.mutableSetValueForKey(key)
        items.addObject(value)
    }

    func removeObject(value: NSManagedObject, forKey key: String) {
        let items = self.mutableSetValueForKey(key)
        items.removeObject(value)
    }
}

which is used like this:

self.addObject(slot, forKey:"timeSlotItems")