从 Core Data 加载 NSManagedObject 时，我是否免费获得它 children？

Question

我正在尝试学习如何在 Core Data 中使用这种奇特的新关系模式来模拟字符串数组。我有一个 Alarm 实体和一个 NotificationUuid 实体。 Alarm是NotificationUuid的parent个实体，因为一个Alarm可以有多个NotificationUuid，一个NotificationUuid只能有一个parent个Alarm。我在我的 .xcdatamodeld 文件中设置了所有这些。

我的问题是：当我像这样获取 parent 警报 object 时：

private func loadAlarms() {

    os_log("loadAlarms() called", log: OSLog.default, type: .debug)
    guard let appDelegate = UIApplication.shared.delegate as? AppDelegate else {
            return
    }
    let managedContext = appDelegate.persistentContainer.viewContext
    let fetchRequest = NSFetchRequest<AlarmMO>(entityName: "Alarm")

    do {
        if self.alarms.count == 0 {
            self.alarms = try managedContext.fetch(fetchRequest)
            os_log("Loading %d alarms", log: OSLog.default, type: .debug, self.alarms.count)
        } else {
            os_log("Didn't need to load alarms", log: OSLog.default, type: .debug)
        }
    } catch let error as NSError {
        print("Could not fetch alarms. \(error), \(error.userInfo)")
    }

}

我可以免费获得 AlarmMO（Alarm Managed Object）object 的 children、NotificationUuid object 吗？还是我现在也必须为他们设置一个获取请求？这整个奇妙的 parent/child 关系是如何运作的，我如何 set/load 来自这些实体的东西？

谢谢

我是这样定义 AlarmMO 的：

import CoreData

@objc(AlarmMO)
public class AlarmMO: NSManagedObject {

    @NSManaged public var alarmNumber: Int64
    @NSManaged public var alarmTime: NSDate?
    @NSManaged public var endTimeInterval: Double
    @NSManaged public var recurrence: Int64
    @NSManaged public var startTimeInterval: Double
    @NSManaged public var notificationUuidChildren: NSSet?


}

// MARK: Generated accessors for notificationUuidChildren
extension AlarmMO {

    @objc(addNotificationUuidChildrenObject:)
    @NSManaged public func addToNotificationUuidChildren(_ value: NotificationUuidMO)

    @objc(removeNotificationUuidChildrenObject:)
    @NSManaged public func removeFromNotificationUuidChildren(_ value: NotificationUuidMO)

    @objc(addNotificationUuidChildren:)
    @NSManaged public func addToNotificationUuidChildren(_ values: NSSet)

    @objc(removeNotificationUuidChildren:)
    @NSManaged public func removeFromNotificationUuidChildren(_ values: NSSet)

}

和 NotificationUuidMO:

import CoreData

@objc(NotificationUuid)
public class NotificationUuidMO: AlarmMO {

    @NSManaged public var notificationUuid: String
    @NSManaged public var alarmParent: AlarmMO

}

Answer 1

当看到你的 AlarmMO 模型时，你可以只获取你的 AlarmMO 模型，它将保存 notificationUuidChildren 集合中 NotificationUuidMO 的列表。所以不需要单独取NotificationUuidMO

而AlarmMO到NotificationUuidMO是一对多的关系。所以你可以从 AlarmMO 得到 notificationUuidChildren ，从 NotificationUuidMO.

得到 alarmParent

要将 NotificationUuidMO 添加到 notificationUuidChildren 集，您可以使用 extension AlarmMO.

中给出的 Core-Data 生成的访问器

示例：

let notificationUuid = NotificationUuidMO....
let alarmMO = AlarmMO....

alarmMO.addToNotificationUuidChildren(notificationUuid)//Here your notificationUuid will be added to `notificationUuidChildren` Set and `alarmParent` of your `notificationUuid` will be automatically assigned to `alarmMO`.

从 Core Data 加载 NSManagedObject 时，我是否免费获得它 children？

When loading an NSManagedObject from Core Data, do I get it's children for free?

entities

core-data

relationship

nsmanagedobject

swift