获取对象时无法访问一对多的CoreData关系

Question

我创建了一个dataModel,我有一个任务.此任务有几个变量,但也有一个与事件的一对多链接.这些事件可能是添加图片或评论等内容,因此一项任务可能会有很多事件.我把它们联系起来,如下所示:

实体文件也设置为:

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?

}

和

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

}

对我来说,这些看起来都很正确,但我可能错了.然后我在我的一个viewControllers中获取所有任务

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!
}

我可以向您保证,managedObjectContext既是最新的,也是正确传递的.如果我尝试访问事件数组,则会出现问题.我使用获取每个任务

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

使用cellForRowAtIndexPath,因为它在tableView中.这再次有效,但是当我尝试let event = foundTask.events[0]或类似的东西时,我得到了一个消息崩溃

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

我已经尝试将数组转换为NSArray并使用像.firstObject这样的函数,并且还将它放入NSSet但它永远不会让我访问事件.看起来当提取任务时,事件不是,因此给出了数据错误.我希望它能在我需要它时获取事件,但同样,它不会这样做.对不起,很长的帖子,但我希望包含尽可能多的信息,因为我觉得你需要帮助我.请询问您是否需要更多信息,我会尽快回复.

非常感谢

Answer 1

Core Data中的(无序)to-many关系表示为NSSet,而不是数组,因此属性应声明为

@NSManaged var events: NSSet

要将集合转换为数组,请使用allObjects:

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

请注意,Xcode可以为您创建托管对象子类(编辑器 - >创建NSManagedObject子类...),我建议您避免这种错误.