核心数据排序描述符与NSDate，iOS与Swift [英] Core Data sort descriptor with NSDate, iOS with Swift

问题描述

我试图根据日期属性过滤核心数据对象。

I am trying to filter core data objects depending on a date attribute.

这是我当前的代码：

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)
}

但我在行中遇到错误：

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

如何更改此排序描述符以获取在timeStamp属性上具有较早或较新日期的对象？

How should I change this sort descriptor to get the objects that have an older or a newer date on the "timeStamp" attribute?

谢谢。

推荐答案

要获取满足某些条件的所有对象，您不需要
描述符而是一个谓词，例如：

To fetch all objects satisfying some condition you don't need a sort descriptor but a predicate, for example:

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

排序描述符以获得指定顺序中的对象
例如：

You need a sort descriptor to get the objects in a specified order, for example:

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

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