如何更新核心数据中的值？

Question

每次尝试学习闪存卡时，我都试图更新其分数，但是分数没有保存。我在做什么错了？

do {

    fetchedCards = try context.fetch(Cards.fetchRequest())

    for cards in fetchedCards {
        if(termLabel.text == cards.term){
            cards.score = score
            ad.saveContext()
            continue
        }
    }

} catch {

}


let ad = UIApplication.shared.delegate as! AppDelegate
let context = ad.persistentContainer.viewContext