使用 NSDate 的核心数据排序描述符，使用 Swift 的 iOS

Posted 2023-03-05

【中文标题】使用 NSDate 的核心数据排序描述符，使用 Swift 的 iOS

【英文标题】：Core Data sort descriptor with NSDate, iOS with Swift

【发布时间】：2015-05-28 16:17:08

【问题描述】：

我正在尝试根据日期属性过滤核心数据对象。

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)

但我在行出现错误：

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

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

谢谢。

【参考方案1】：

要获取满足某些条件的所有对象，您不需要 排序描述符但一个谓词，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顺序获取对象， 例如：

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

【讨论】：

¿如何更改指定顺序（排序描述符）并刷新 NSFetchedResultsController 以显示结果？

【参考方案2】：

Swift 3.0 这对我来说没有问题

let fec:NSFetchRequest = YourEntity.fetchRequest()
let sortDescriptor = NSSortDescriptor(key: "type", ascending: true)
fec.sortDescriptors = [sortDescriptor]
let items = try! context.fetch(fec)

【参考方案3】：

>Swift4

func getLastDateFromEntries(entityName:String) -> [NSManagedObject]
    let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
    do 
        let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: entityName)
        let sortDescriptors = NSSortDescriptor(key: "dueDate", ascending: false) // dueDate is key
        fetchRequest.sortDescriptors = [sortDescriptors]
        fetchRequest.fetchLimit = 1 // add limit
        let fetchedResults = try context.fetch(fetchRequest) as! [NSManagedObject]
        return fetchedResults
    
    catch 
        print ("fetch task failed", error)
        return []