如何将我的卡转换为NSSet？

Question

I am trying to add a new Card to a Deck of cards, but am running into an issue when trying to save my card to the deck's cards . How do I convert it to an NSSet ?

func saveQA(question: String, answer: String) {
    let currentDeckName = deckName
    let entity = NSEntityDescription.entityForName("Card", inManagedObjectContext: managedContext)
    let newQA = Card(entity: entity!, insertIntoManagedObjectContext: managedContext)
    newQA.question = question
    newQA.answer = answer
    currentDeckName!.cards = newQA

    do {
        try managedContext.save()
        userCards.append(newQA)
    }
    catch {
        let saveError = error as NSError
        print(saveError)
    }
}

Answer 1

Here, you're trying to assign a Card to a property that is expecting an NSSet . A card is not a set (although it could be an object in a set).

currentDeckName!.cards = newQA

Taking advantage of type safety

Since you are coding in Swift, the first thing you should do is use Swift types such as Set instead of NSSet . In your Deck+CoreDataProperties.swift , change your relationship from NSSet? to a typed set of cards.

@NSManaged var cards: Set<Card>

This not only tells Swift that cards is a Set, but also specifies that the objects in the set will be Card s.

You always want to declare specific types for relationships to benefit from the language's type safety. This allows the compiler to prevent you from ever adding anything other than a Card to the deck's set of cards.

Adding a card to the deck

You could use the usual Set methods such as insert to insert a card into a deck's set.

currentDeckName.cards.insert(newQA)

However, a much easier way is to use the reverse relationship on the card itself. In other words, tell the new card that it belongs to this deck:

newQA.deck = currentDeckName

That will automatically add the card to the deck's set of cards.

It's a bit less code, and less is generally better to read and understand.

Speaking of readability, you may want to consider renaming currentDeckName to currentDeck since that object is a Deck , not the name of a deck.

Answer 2

For converting your object to MutableSet please verify with following step.

1) Select your model object
2) select your parent entity
3) Select Relationship which is one To many
4) now check following image property is one To many or not.