核心数据排序描述符与NSDate,iOS与Swift

Question

我试图根据日期属性过滤核心数据对象.

这是我目前的代码:

func getFetchedResultController(selectedEntity: NSString){

    let appDelegate : AppDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
    let managedObjectContext: NSManagedObjectContext = appDelegate.managedObjectContext!

    let fetchRequest = NSFetchRequest()

    let entity = NSEntityDescription.entityForName(selectedEntity as String, inManagedObjectContext: managedObjectContext)

    fetchRequest.entity = entity

    fetchRequest.fetchBatchSize = 20

    let date = NSDate()

    let sectionSortDescriptor = NSSortDescriptor(key: "timeStamp < %@",date)

    let sortDescriptors = [sectionSortDescriptor] //, secondSortDescriptor]

    fetchRequest.sortDescriptors = sortDescriptors

    let aFetchedResultsController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: managedObjectContext, sectionNameKeyPath: nil, cacheName: nil)

    aFetchedResultsController.delegate = self
    self.fetchedResultsController = aFetchedResultsController

    var error: NSError? = nil
    if !self.fetchedResultsController.performFetch(&error) {
        abort()
    }

 print(fetchedResultsController.fetchedObjects?.count ?? 0)
}

但我得到一个错误:

let sectionSortDescriptor = NSSortDescriptor(key: "timeStamp < %@",date)

我应该如何更改此排序描述符以获取"timeStamp"属性上具有较旧或较新日期的对象？

谢谢.

Answer 1

要获取满足某些条件的所有对象,您不需要排序描述符而是谓词,例如:

let predicate = NSPredicate(format: "timeStamp < %@", date)
fetchRequest.predicate = predicate

您需要一个排序描述符来按指定的顺序获取对象,例如:

let sectionSortDescriptor = NSSortDescriptor(key: "timeStamp", ascending: true)
let sortDescriptors = [sectionSortDescriptor]
fetchRequest.sortDescriptors = sortDescriptors