One to many CoreData relationship cannot be accessed when the object is fetched

Question

I have created a dataModel where I have a task. This task has several variables but also has a one-many link with events. These events could be things like pictures or comments being added and so there may be many events to one task. I have linked them up as shown below:

The entity files are also setup:

import CoreData

class Task: NSManagedObject {

    @NSManaged var area : Area
    @NSManaged var pictures : [TaskPicture]
    @NSManaged var events : [Event]

    @NSManaged var requestedByDept : NSString?
    @NSManaged var requestedByUser : NSString?
    @NSManaged var workloadDept : NSString?
    @NSManaged var detailDescription : NSString?
    @NSManaged var status : NSString
    @NSManaged var uniqueId : NSString?
    @NSManaged var isActive : NSNumber
    @NSManaged var created : NSDate?
    @NSManaged var modified : NSDate?
    @NSManaged var thumbnail : NSData?

}

and

import CoreData

class Event: NSManagedObject {


    @NSManaged var task : Task

    @NSManaged var actionBy : NSString?
    @NSManaged var detailDescription : NSString?
    @NSManaged var status : NSString
    @NSManaged var uniqueId : NSString?
    @NSManaged var isActive : NSNumber
    @NSManaged var created : NSDate?
    @NSManaged var modified : NSDate?
    @NSManaged var type : NSString

}

To me, these all look correct but i may be wrong. I then fetch all of the tasks in one of my viewControllers

var fetchedResultsController: NSFetchedResultsController {
    if _fetchedResultsController != nil {
        return _fetchedResultsController!
        }

        let fetchRequest = NSFetchRequest()
        let entity = NSEntityDescription.entityForName("Task", inManagedObjectContext: self.managedObjectContext)
        fetchRequest.entity = entity

        fetchRequest.fetchBatchSize = 20

        let sortDescriptor = NSSortDescriptor(key: "created", ascending: false)

        fetchRequest.sortDescriptors = [sortDescriptor]

        let aFetchedResultsController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: self.managedObjectContext, sectionNameKeyPath: nil, cacheName: nil)
        aFetchedResultsController.delegate = self
        _fetchedResultsController = aFetchedResultsController

        var error: NSError? = nil
        if !_fetchedResultsController!.performFetch(&error) {
            println("Unresolved error \(error)")
            abort()
        }

        return _fetchedResultsController!
}

I can assure you that the managedObjectContext is both up-to-date and passed in correctly. The problem then occurs if I try to access the events array. I fetch each of the tasks using

let foundTask : Task = self.fetchedResultsController.objectAtIndexPath(indexPath) as Task

using cellForRowAtIndexPath as it is in a tableView. This again works but then when i try let event = foundTask.events[0] or something similar, i get a crash with the message

-[_NSFaultingMutableSet objectAtIndex:]: unrecognized selector sent to instance 0x17022e9c0

I have tried both casting the array as an NSArray and using the functions like .firstObject, and have also put it into an NSSet but it never lets me access the events. It seems like when the Tasks are fetched, the events are not, hence giving a data fault. I would expect it to fetch the events when i need them but again, it does not do so. Sorry for the long post, but i wanted to include as much information as I felt you would need to help me. Please ask if you need any more information and i will try to reply as quickly as possible.

Thanks a lot

Answer 1

A (unordered) to-many relationship in Core Data is represented as NSSet, not as an array, so the property should be declared as

@NSManaged var events: NSSet

To convert the set to an array use allObjects:

let events = foundTask.events.allObjects as [Event]

Note that Xcode can create the managed object subclasses for you (Editor -> Create NSManagedObject Subclass...), which I would recommend to avoid this kind of error.