如何在 Swift 中从核心数据中获取 NSSet

Question

我有一个 Person 类和一个 Brand 类，它们是 Core Data 中的关系。我知道如何获取整个 Person 类 (NSManagedObject)，但我如何深入研究以仅获取与该人关联的品牌？

    import Foundation
    import CoreData

    class Person: NSManagedObject {

        @NSManaged var name: String
        @NSManaged var brands: NSSet

        func addBrandsObject(value: Brand) {
            self.mutableSetValueForKey("brands").addObject(value)
        }

    }

import Foundation
import CoreData

class Brand: NSManagedObject {

    @NSManaged var name: String
    @NSManaged var people: NSSet


}

视图控制器：

![import UIKit
import CoreData

    class BrandsTableTableViewController: UITableViewController {


        var brands = \[NSManagedObject\]()
        var selectedPerson: Person?
        var selectedBrand: Brand?

        //Fetch Core Data
        override func viewWillAppear(animated: Bool) {
            super.viewWillAppear(animated)
            self.fetchCoreData()
        }

        //Helper Function to Fetch Core Data
        func fetchCoreData() {
            //1
            let appDelegate =
            UIApplication.sharedApplication().delegate as! AppDelegate

            let managedContext = appDelegate.managedObjectContext!

            //2
            let fetchRequest = NSFetchRequest(entityName:"Person")

            //3
            var error: NSError?

            let fetchedResults =
            managedContext.executeFetchRequest(fetchRequest,
                error: &error) as? \[NSManagedObject\]

            if let results = fetchedResults {
                ////what here? 
            } else {
                println("Could not fetch \(error), \(error!.userInfo)")
            }
        }][1]

Answer 1

由于您已经拥有 person 实例，因此只需访问关系：

    for person in results {
        let brandSet = person.brands
    }

无需获取。

这当然是假设您从Person 到Brand 的关系称为brands。

还会有一些施法，没有施法就不能快速......

Answer 2

您需要告诉它您正在获取的是“Person”对象，然后您可以遍历品牌。

//Helper Function to Fetch Core Data
func fetchCoreData() {
    //1
    let appDelegate =
    UIApplication.sharedApplication().delegate as! AppDelegate

    let managedContext = appDelegate.managedObjectContext!

    //2
    let fetchRequest = NSFetchRequest(entityName:"Person")

    //3
    var error: NSError?

    var people =
        managedContext.executeFetchRequest(fetchRequest,
        error: &error) as! [Person]

    // Get all brands from all people
    for (var x=0; x<people.count; x++) {
        let brands: NSArray = people[x].brands.allObjects

        for brand in brands {
            println(brand.name)
        }
    }
}