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

Did you add relationships in the XCDataModel? – Harsh Aug 11 '16 at 19:46 — Harsh, Aug 11 '16 at 19:46
Yes i set one to many relationship with inverse for item – Lê Khánh Vinh Aug 11 '16 at 23:22 — Lê Khánh Vinh, Aug 11 '16 at 23:22

score 2 · Accepted Answer · answered Aug 12 '16 at 09:37

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()
    }

Hi Thanks for your help. I can add relationship now. The tricky part is to use Set instead of the default NSSet. Is this a bug? In objectiveC I can use Xcode to generate NSManageSubclass working find but in Swift the relation to own entity seem not working automatically — Lê Khánh Vinh, Aug 12 '16 at 12:29
It is not a bug, but it is easier than using NSSet & getting mutable copy of it then save it back again. — Mohamed Mostafa, Aug 12 '16 at 14:44

score 0 · Answer 2 · edited May 23 '17 at 12:32

0

Try this to automatically create relationships and properties.

Generating Swift models from Core Data entities

i.e. Edit: I found the solution to generate a Swift model from Core Data entity:

On Xcode:

Editor > Create NSManagedOjbect > Click button "Next" > Click button "Next" > Select "Swift" Langage > Click button "Create"

Here is the link on how to create a relationship from scratch. This is a very well explained and awesome tutorial. Go through this and you'll be able to understand all the things. http://code.tutsplus.com/tutorials/core-data-from-scratch-relationships-and-more-fetching--cms-21505

edited May 23 '17 at 12:32

Community

1
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answered Aug 12 '16 at 00:37

Harsh

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Hi i already created using that. But how to add item to the set for examle item.kids.add(kid) or something similar – Lê Khánh Vinh Aug 12 '16 at 01:29
Hi thanks for your help. I know how to create relationship. But my problem is to add item to relationship to own entity. I have uploaded picture of my coredata and generated NSmanage Object to question. but cannot add item to kids (NSSet property) – Lê Khánh Vinh Aug 12 '16 at 03:20

swift core data relationship one to many for own entity

2 Answers2