swift core data relationship one to many for own entity

Question

Hi I'm building a newspaper database which have item relationship to itself (item can have many other item as child)

here is my NSmanageObjectSubclass

import Foundation
import CoreData
extension Item {

    @NSManaged var by: String?
    @NSManaged var dead: NSNumber?
    @NSManaged var descendants: NSNumber?
    @NSManaged var id: NSNumber?
    @NSManaged var isdeleted: NSNumber?
    @NSManaged var score: NSNumber?
    @NSManaged var text: String?
    @NSManaged var time: NSDate?
    @NSManaged var title: String?
    @NSManaged var type: String?
    @NSManaged var url: String?
    @NSManaged var kids: NSSet?
    @NSManaged var parent: Item?
    @NSManaged var parts: NSSet?

}

Problem is that how can i add item to property kids: NSSet the relationship define is one to many to its own with reverse. Any help is much appreciate. Thanks.

my coredata xcmodel

Answer 1

First update your class Managed Object class to use Sets instead of NSSet

     import Foundation
        import CoreData
        extension Item {

            @NSManaged var by: String?
            @NSManaged var dead: NSNumber?
            @NSManaged var descendants: NSNumber?
            @NSManaged var id: NSNumber?
            @NSManaged var isdeleted: NSNumber?
            @NSManaged var score: NSNumber?
            @NSManaged var text: String?
            @NSManaged var time: NSDate?
            @NSManaged var title: String?
            @NSManaged var type: String?
            @NSManaged var url: String?
            @NSManaged var kids: Set<Item>
            @NSManaged var parent: Item?
            @NSManaged var parts: NSSet?

        }

Secondly create a fetchRequest named getItemByID with expression id == $ID

Third create a function to get item by id

    func getItemById(ID:String) -> Item?
    {
        let fetchRequest : NSFetchRequest = self.managedObjectModel.fetchRequestFromTemplateWithName("getItemByID", substitutionVariables: ["ID": ID])!
        do {
            let fetchedResult = try managedObjectContext!.executeFetchRequest(fetchRequest) as! [Item]
            if fetchedResult.count > 0 {
                let result = fetchedResult[0]
                return result
            }
        }
        catch {
            print("Could not fetch \(error)")
        }
        return nil
    }

After that you have many options to set relations

a) you create relation after adding parent & child to coreData

func addChildToParent(childID:String,parentID:String)
    {
        if let childItem = getItemById(childID)
        {
           if let parentItem = getItemById(parentID)
           {
              parentItem.kids.insert(menuItemCatering)
              childItem.parent = parentItem
           }
        }
       saveContext()
    }