Ios 使用swift将Json转换为CoreData-CoreData:错误：未能调用NSManagedObject类上指定的初始值设定项

请知道有人告诉我我做错了什么吗？
应用程序崩溃：
CoreData:错误：调用NSManagedObject类上指定的初始值设定项失败“xyz.Topics”
我需要JSON解析和存储到CoreData的帮助

import CoreData


class Topics: NSManagedObject {

    @NSManaged var id: NSNumber
    @NSManaged var name: NSString
    @NSManaged var price: NSNumber
    @NSManaged var subject_id: NSNumber
    @NSManaged var created_at: NSDate
    @NSManaged var updated_at: NSDate
    @NSManaged var deleted_at: NSDate

    func parseData (){
        var endpoint = NSURL(string: "......")
        var data = NSData(contentsOfURL: endpoint!)



        let json = NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions.MutableContainers, error: nil) as NSDictionary

        var items = [[String:AnyObject]()]
        var item:AnyObject

        for (var i = 0; i < json["topics"]!.count; i++) {

            items.append([String:AnyObject]())

            item = json["topics"]![i] as NSDictionary

                items[i]["id"] = item["id"] as? NSNumber

                items[i]["name"] = item["name"] as? String

                items[i]["price"] = item["price"] as? NSNumber

                items[i]["subject_id"] = item["subject_id"] as? NSNumber

                items[i]["deleted_at"] = item["deleted_at"] as? NSDate

                items[i]["created_at"] = item["created_at"] as? NSDate

                items[i]["updated_at"] = item["updated_at"] as? NSDate

                //Save
                var addTopicItem = NSEntityDescription.insertNewObjectForEntityForName("Topics", inManagedObjectContext: managedObjectContext!) as NSManagedObject

                addTopicItem.setValue(items[i]["id"], forKey: "id")

                addTopicItem.setValue(items[i]["name"], forKey: "name")

                addTopicItem.setValue(items[i]["price"], forKey: "price")

                addTopicItem.setValue(items[i]["subject_id"], forKey: "subject_id")

                addTopicItem.setValue(items[i]["deleted_at"], forKey: "deleted_at")

                addTopicItem.setValue(items[i]["created_at"], forKey: "created_at")

                addTopicItem.setValue(items[i]["updated_at"], forKey: "updated_at")

                managedObjectContext!.save(nil)

    }
    }

}

// MARK: - Core Data stack

lazy var applicationDocumentsDirectory: NSURL = {
    // The directory the application uses to store the Core Data store file. This code uses a directory named "xyz" in the application's documents Application Support directory.
    let urls = NSFileManager.defaultManager().URLsForDirectory(.DocumentDirectory, inDomains: .UserDomainMask)
    return urls[urls.count-1] as NSURL
}()

lazy var managedObjectModel: NSManagedObjectModel = {
    // The managed object model for the application. This property is not optional. It is a fatal error for the application not to be able to find and load its model.
    let modelURL = NSBundle.mainBundle().URLForResource("xyz", withExtension: "momd")!
    return NSManagedObjectModel(contentsOfURL: modelURL)!
}()

lazy var persistentStoreCoordinator: NSPersistentStoreCoordinator? = {
    // The persistent store coordinator for the application. This implementation creates and return a coordinator, having added the store for the application to it. This property is optional since there are legitimate error conditions that could cause the creation of the store to fail.
    // Create the coordinator and store
    var coordinator: NSPersistentStoreCoordinator? = NSPersistentStoreCoordinator(managedObjectModel: self.managedObjectModel)
    let url = self.applicationDocumentsDirectory.URLByAppendingPathComponent("xyz.sqlite")
    var error: NSError? = nil
    var failureReason = "There was an error creating or loading the application's saved data."
    if coordinator!.addPersistentStoreWithType(NSSQLiteStoreType, configuration: nil, URL: url, options: nil, error: &error) == nil {
        coordinator = nil
        // Report any error we got.
        var dict = [String: AnyObject]()
        dict[NSLocalizedDescriptionKey] = "Failed to initialize the application's saved data"
        dict[NSLocalizedFailureReasonErrorKey] = failureReason
        dict[NSUnderlyingErrorKey] = error
        error = NSError(domain: "YOUR_ERROR_DOMAIN", code: 9999, userInfo: dict)
        // Replace this with code to handle the error appropriately.
        // abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
        NSLog("Unresolved error \(error), \(error!.userInfo)")
        abort()
    }

    return coordinator
}()

lazy var managedObjectContext: NSManagedObjectContext? = {
    // Returns the managed object context for the application (which is already bound to the persistent store coordinator for the application.) This property is optional since there are legitimate error conditions that could cause the creation of the context to fail.
    let coordinator = self.persistentStoreCoordinator
    if coordinator == nil {
        return nil
    }
    var managedObjectContext = NSManagedObjectContext()
    managedObjectContext.persistentStoreCoordinator = coordinator
    return managedObjectContext
}()

// MARK: - Core Data Saving support

func saveContext () {
    if let moc = self.managedObjectContext {
        var error: NSError? = nil
        if moc.hasChanges && !moc.save(&error) {
            // Replace this implementation with code to handle the error appropriately.
            // abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
            NSLog("Unresolved error \(error), \(error!.userInfo)")
            abort()
        }
    }
}