我有一个Destination类型的实体…

import Foundation
import CoreData

class Destination: NSManagedObject {
    @NSManaged var name: String
    @NSManaged var location: Location
}

…具有简单的名称属性(String类型)和类型为Location的属性：

import Foundation

class Location: NSObject,NSCoding {
    var address: String
    var latitude: Double
    var longitude: Double

    required init?(coder aDecoder: NSCoder) {
        address = aDecoder.decodeObjectForKey("Address") as? String ?? ""
        latitude = aDecoder.decodeObjectForKey("Latitude") as? Double ?? 0.0
        longitude = aDecoder.decodeObjectForKey("Longitude") as? Double ?? 0.0
        super.init()
    }

    init(address: String,latitude: Double,longitude: Double) {
        self.address = address
        self.latitude = latitude
        self.longitude = longitude

        super.init()
    }

    func encodeWithCoder(aCoder: NSCoder) {
        aCoder.encodeObject(address,forKey: "Address")
        aCoder.encodeObject(latitude,forKey: "Latitude")
        aCoder.encodeObject(longitude,forKey: "Longitude")
    }
}

位置在Core Data中配置为“可转换”,因为它具有其他基本类型都无法处理的结构.

使用Apple的样板核心数据代码,这里是一个视图控制器,它只执行以下操作：

>获取必要的appDelegate / ManagedApplicationContext引用
>如果存在目的地,则获取目的地,否则创建一个目的地
>打印目的地的名称和location.address
>更新目标的名称和location.address
>保存对ManagedObjectContext的更改

当应用程序运行并重新运行时,只会对名称进行更改.对location.address所做的更改不会保留.

import UIKit
import CoreData

class ViewController: UIViewController {

    var appDelegate: AppDelegate!
    var context: NSManagedObjectContext!

    override func viewDidLoad() {
        super.viewDidLoad()
        updateDestination()
    }

    func updateDestination() {
        var destination: Destination
        appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
        context = appDelegate.managedObjectContext

        if let dest = fetchOneDestination() {
            destination = dest
        }
        else {
            destination = create()!
        }
        print("destination named: \(destination.name),at: \(destination.location.address)")

        destination.name = "New name of place that will update and persist"
        destination.location.address = "123 main st (change that will never persist)"
        appDelegate.saveContext()
    }

    func create() -> Destination? {
        guard let newDestination = NSEntityDescription.insertNewObjectForEntityForName("Destination",inManagedObjectContext: context) as? Destination else {
            return nil
        }
        newDestination.name = "Original name of place that can be updated"
        newDestination.location = Location(address: "100 main st",latitude: 34.051145,longitude: -118.243595)
        return newDestination
    }

    func fetchOneDestination() -> Destination? {
        let request = NSFetchRequest()
        request.entity = NSEntityDescription.entityForName("Destination",inManagedObjectContext: context)
        do {
            let fetchResults = try context.executeFetchRequest(request)
            if fetchResults.count > 0 {
                if let dest = fetchResults[0] as? Destination {
                    return dest
                }
            }
        }
        catch {}
        return nil
    }
}

如何更新目标的位置属性？