Core-Data Swift大约一对一的关系

Question

我注入了托管上下文来保存和获取实体，我很满意。我的问题是如何获得与1对1关系相关的数据？

以下是代码，请参阅viewDidLoad中的注释：

import UIKit
import CoreData

class E2_VC: UIViewController {

  var managedContext: NSManagedObjectContext!
  var selectedE1: Entity_1!
  var selectedE2: Entity_2!

  // MARK: Properties
  @IBOutlet weak var e2_a1: UITextField!
  @IBOutlet weak var e2_a2: UITextField!
  @IBOutlet weak var e2_a3: UITextField!
  @IBOutlet weak var e4_a1: UITextField!
  @IBOutlet weak var e4_a2: UITextField!
  @IBOutlet weak var e5_a1: UITextField!
  @IBOutlet weak var e5_a2: UITextField!


  override func viewDidLoad() {
    super.viewDidLoad()

    print(selectedE1)
    print(selectedE2)

    e2_a1.text = selectedE2.attribute1
    e2_a2.text = selectedE2.attribute2
    e2_a3.text = selectedE2.attribute3

    // I want to get something like "e4_a1.text = selectedE2.e4_to_e2.attribute1"
    // but obviously it is not working like that, what am I missing here?
    // I'm thinking about making a fetch request but I don't know how to 
    // make a fetch req that specifically belongs to the selectedE2 onbejct.

  }

  override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
  }

  // MARK: - Navigation
  func navigateBack(){
    let isCurrentNavContrl = presentingViewController is UINavigationController
    if isCurrentNavContrl {
      dismissViewControllerAnimated(true, completion: nil)
    } else {
      navigationController!.popViewControllerAnimated(true)
    }
  }

  // MARK: - Save
  @IBAction func save(sender: UIBarButtonItem) {
    let newE2 = NSEntityDescription.entityForName("Entity_2", inManagedObjectContext: managedContext)
    let newE4 = NSEntityDescription.entityForName("Entity_4", inManagedObjectContext: managedContext)
    let newE5 = NSEntityDescription.entityForName("Entity_5", inManagedObjectContext: managedContext)

    if selectedE1 != nil {
      do {
        let ent2 = Entity_2(entity: newE2!, insertIntoManagedObjectContext: managedContext)
        let ent4 = Entity_4(entity: newE4!, insertIntoManagedObjectContext: managedContext)
        let ent5 = Entity_5(entity: newE5!, insertIntoManagedObjectContext: managedContext)

        ent2.attribute1 = e2_a1.text!
        ent2.attribute2 = e2_a2.text!
        ent2.attribute3 = e2_a3.text!

        ent4.attribute1 = e4_a1.text!
        ent4.attribute2 = e4_a2.text!
        ent2.e2_to_e4 = ent4
        ent4.e4_to_e2 = ent2

        ent5.attribute1 = e5_a1.text!
        ent5.attribute2 = e5_a2.text!
        ent2.e2_to_e5 = ent5

        try managedContext.save()
      } catch let error as NSError {
        print("Error: \(error) " + "description \(error.localizedDescription)")
      }
    } else {

      do {
        selectedE2.attribute1 = e2_a1.text!
        selectedE2.attribute2 = e2_a2.text!
        selectedE2.attribute3 = e2_a3.text!

        try managedContext.save()
      } catch let error as NSError {
        print("Error: \(error) " + "description \(error.localizedDescription)")
      }
    }


    navigateBack()
  }

  @IBAction func cancel(sender: UIBarButtonItem) {
    navigateBack()
  }

}

这条线说的是什么（我的意思是我不太明白什么是关系错误）？

"e1_to_e2" = "<relationship fault: 0x7fbf995e3800 'e1_to_e2'>";

这一个;我没有设置e2_to_e1。我认为核心数据会将其设置为我将其设置为e1_to_e2关系的反转。

"e2_to_e1" = nil;

以下是控制台上的 selectedE1 和 selectedE2 输出：

<iTMJ_CD_93.Entity_1: 0x7fbf9b04ef20> (entity: Entity_1; id: 0xd000000000080000 <x-coredata://F20092F3-5A36-49C3-9AAD-3F1E132CD538/Entity_1/p2> ; data: {
    attribute1 = a;
    attribute2 = s;
    attribute3 = d;
    "e1_to_e2" = "<relationship fault: 0x7fbf995e3800 'e1_to_e2'>";
})
<iTMJ_CD_93.Entity_2: 0x7fbf9962c670> (entity: Entity_2; id: 0xd000000000040002 <x-coredata://F20092F3-5A36-49C3-9AAD-3F1E132CD538/Entity_2/p1> ; data: {
    attribute1 = e2a1;
    attribute2 = e2a2;
    attribute3 = e2a3;
    date = nil;
    "e2_to_e1" = nil;
    "e2_to_e3" = "<relationship fault: 0x7fbf995e6940 'e2_to_e3'>";
    "e2_to_e4" = "0xd000000000040004 <x-coredata://F20092F3-5A36-49C3-9AAD-3F1E132CD538/Entity_4/p1>";
    "e2_to_e5" = "0xd000000000040006 <x-coredata://F20092F3-5A36-49C3-9AAD-3F1E132CD538/Entity_5/p1>";
})

这是我的数据模型：

enter image description here