\'NSSet\' 类型的值没有成员 \'_\' - 无法通过 NSSet 访问属性答案

【问题标题】：Value of type 'NSSet' has no member '_' - Unable to Access attributes through NSSet\'NSSet\' 类型的值没有成员 \'_\' - 无法通过 NSSet 访问属性
【发布时间】：2022-12-06 05:31:32
【问题描述】：

我有一个由 3 个实体设置的核心数据模型：Exercise、ExerciseSet 和 Workout。它的设置使 Exercise 和 ExerciseSet 具有一对一的关系，而 Workout 和 ExerciseSet 具有一对多的关系。我正在尝试通过 Workout 访问 ExerciseSet 中的属性，但是当我运行此代码时：

struct WorkoutView: View {
@State var workout = Workout()
    
    var body: some View {
        
        Text("Sets in Workout: \(workout.exerciseSets.count)")
        
        ForEach(Array(arrayLiteral: workout.exerciseSets), id: \.self) { e in
            Text("Exercise Name: \(e.exercise.exercisename), Reps: \(e.reps), Weight: \(e.weight)")         
        }

我收到以下错误

Value of type 'NSSet' has no member 'exercise'
Value of type 'NSSet' has no member 'reps'
Value of type 'NSSet' has no member 'weight'

当我在锻炼之外调用它们并且 workout.exerciseSets.count 按预期返回时，这些属性都存在。

以下是每个实体的定义：

extension Exercise {

    @nonobjc public class func fetchRequest() -> NSFetchRequest<Exercise> {
        return NSFetchRequest<Exercise>(entityName: "Exercise")
    }

    @NSManaged public var exercisename: String
    @NSManaged public var id: UUID?
    @NSManaged public var musclegroup: String?
    @NSManaged public var exerciseSet: ExerciseSet?

}

extension Exercise : Identifiable {

}

extension ExerciseSet {

    @nonobjc public class func fetchRequest() -> NSFetchRequest<ExerciseSet> {
        return NSFetchRequest<ExerciseSet>(entityName: "ExerciseSet")
    }

    @NSManaged public var dateCompleted: Date
    @NSManaged public var id: UUID?
    @NSManaged public var reps: Int16
    @NSManaged public var weight: Int16
    @NSManaged public var exercise: Exercise
    @NSManaged public var workout: Workout?

}

extension ExerciseSet : Identifiable {

}

extension Workout {

    @nonobjc public class func fetchRequest() -> NSFetchRequest<Workout> {
        return NSFetchRequest<Workout>(entityName: "Workout")
    }

    @NSManaged public var id: UUID
    @NSManaged public var notes: String?
    @NSManaged public var workoutDate: Date
    @NSManaged public var workoutMuscleGroup: String?
    @NSManaged public var workoutName: String?
    @NSManaged public var exerciseSets: NSSet
    
    public var exerciseSetArray: [ExerciseSet] {
        let set = exerciseSets as? Set<ExerciseSet> ?? []
        return set.sorted {
            $0.dateCompleted < $1.dateCompleted
        }
        
    }

}

// MARK: Generated accessors for exerciseSets
extension Workout {

    @objc(addExerciseSetsObject:)
    @NSManaged public func addToExerciseSets(_ value: ExerciseSet)

    @objc(removeExerciseSetsObject:)
    @NSManaged public func removeFromExerciseSets(_ value: ExerciseSet)

    @objc(addExerciseSets:)
    @NSManaged public func addToExerciseSets(_ values: NSSet)

    @objc(removeExerciseSets:)
    @NSManaged public func removeFromExerciseSets(_ values: NSSet)

}

extension Workout : Identifiable {

}

为了能够通过 Workout 访问 ExerciseSet 中的属性，我是否缺少某些东西？谢谢你。

【问题讨论】：

标签： xcode swiftui core-data nsset

【解决方案1】：

Swift 中的NSSet 不知道底层类型。

将 Array(arrayLiteral: workout.exerciseSets) 替换为 workout.exerciseSetArray。

必须将 NSSet 转换为本机 Set<ExerciseSet> 才能访问属性。或者 - 更简单 - 将 exerciseSets 声明为 Set<ExerciseSet>。 Core Data 与原生 Swift 类型配合得很好。

【讨论】：