使用谓词访问一对多 CoreData答案

【问题标题】：Access one to many CoreData with predicate使用谓词访问一对多 CoreData
【发布时间】：2017-05-09 06:35:43
【问题描述】：

我有一个一对多的数据库（问题--->>按钮）我被困在这里，因为我不知道如何继续访问数据库中的按钮：

我有以下代码可以访问我的Questions 实体，但我不知道如何从这里开始。谢谢

 func presentQuestionDetails(questionID :Int) {

        let coreDataStack = CoreDataStack()
        managedObjectContext = coreDataStack.persistentContainer.viewContext

        let fetchRequest: NSFetchRequest<Questions> = Questions.fetchRequest()

         let myPredicate = NSPredicate(format: "%K == %i", "questionID", questionID)
        fetchRequest.predicate = myPredicate

        do {
            let results = try managedObjectContext!.fetch(fetchRequest)

            if results.isEmpty  {
               //empty

                print("empty")
            }

            else {
                let question = results[0]

               //do something
                print("got something")
                questionLabel.text = question.questionTitle

                for _ in 0..<(question.buttons?.count)! {


                    //I'D LIKE TO LOOP THROUGH MY BUTTONS HERE AND ACCESS MY "buttonTitle" i.e print(buttons.buttonTitle!)



                }

            }


        } catch {
            // Replace this implementation with code to handle the error appropriately.
            // fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
            let nserror = error as NSError
            fatalError("Unresolved error \(nserror), \(nserror.userInfo)")
        }



    }

【问题讨论】：

标签： sqlite core-data swift3 nspredicate

【解决方案1】：

这是正确的方法吗？我只是在猜测，并希望得到您的意见。它似乎提供了正确的结果，但我不确定这是否是正确的方法......

谢谢

[...]

 else {
                let question = results[0]

           //do something
            print("got something")
            questionLabel.text = question.questionTitle

                let fetchRequest: NSFetchRequest<Buttons> = Buttons.fetchRequest()
                let myPredicate = NSPredicate(format: "%K == %i", "questions", questionID)
                fetchRequest.predicate = myPredicate

                do {
                    let results = try managedObjectContext!.fetch(fetchRequest)

                     for buttons in results {
                        print(buttons.buttonTitle!)

                    }
                }

                catch {
                    let nserror = error as NSError
                    fatalError("Unresolved error \(nserror), \(nserror.userInfo)")
                }    

            }

【讨论】：