Saving CoreData to-many relationships in Swift

问题

I have a one-to-many relationship that looks like so,

I've set up my model classes in a file to match:

import CoreData
import Foundation

class Board: NSManagedObject {
    @NSManaged var boardColor: String
    @NSManaged var boardCustomBackground: AnyObject?
    @NSManaged var boardID: String
    @NSManaged var boardName: String
    @NSManaged var lists: NSSet
}

class List: NSManagedObject {
    @NSManaged var listID: String
    @NSManaged var listName: String
    @NSManaged var board: Board
}

Because I'm fetching data from multiple JSON endpoints, I have to save my lists seperately from my boards. What I want to do is create/update a list for a board with a matching boardID.

Here's where I am after multiple attempts:

func saveList(boardID: String, listName: String, listID: String) {
    let request = NSFetchRequest(entityName: "Board")
    var error: NSError? = nil
    request.predicate = NSPredicate(format: "boardID like %@", boardID)
    let results: NSArray = context.executeFetchRequest(request, error: &error)
    if results.count > 0 {
        for result in results {
            let board = result as Board
            let list = NSEntityDescription.insertNewObjectForEntityForName("List", inManagedObjectContext: context) as List
            println("💃 want to save \(listName) in \(board.boardName)")
            board.lists.addListObject(lists)
            list.listName = listName
            list.listID = listID
        }
    }
}

Based on Defining CoreData Relationships in Swift and this, I tried to implement @Keenle's answer for define list objects inside a board:

import Foundation

extension Board {
    func addListObject(value:List) {
        var items = self.mutableSetValueForKey("lists");
        items.addObject(value)
    }

    func removeListObject(value:List) {
        var items = self.mutableSetValueForKey("lists");
        items.removeObject(value)
    }
}

However, I ran into the following error at board.lists.addListObject(lists): 'NSSet' does not have a member named 'addListObject'`

Instead of board.lists.addListObject(lists), I also tried board.lists.listName = listName as implied in this Obj-C example, but that sadly didn't work either.

(Also, The println output is correctly specifying the right board and list.)

Thanks in advance!

回答1:

In a one-to-many relationship, it is easier to set the "to-one" direction of the inverse relationships, in your case just

list.board = board

so that the extension methods are actually not needed here.

回答2:

You should invoke addListObject(...) on board object:

board.addListObject(list) // notice that we pass just one object

Additionaly, if you want to be able to add a set of lists to particular board object, you can enhance you Board class extension with methods that accept set of objects:

func addList(values: NSSet) {
    var items = self.mutableSetValueForKey("lists");
    for value in values {
        items.addObject(value)
    }
}

func removeList(values: NSSet) {
    var items = self.mutableSetValueForKey("lists");
    for value in values {
        items.removeObject(value)
    }
}