How to fetch NSSet from Core Data in Swift - ios

Question

I have a Person class and a Brand class that are a relationship in Core Data. I know how to fetch the entire Person class (NSManagedObject), but how do I drill down to only fetch the brand associated with the person?
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
}
Viewcontroller:
![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

Since you already have the person instance, just access the relationship:
for person in results {
let brandSet = person.brands
}
No fetch required.
This is assuming of course that your relationship from Person to Brand is called brands.
There will also be some casting to go around, can't have swift without casting...

Answer 2

You need to tell it that what you are fetching is a "Person" object and then you can iterate through brands.
//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)
}
}
}