Swift 中的核心数据:只在 for 循环中保存最后一个对象

问题描述

我正在尝试在 for 循环中将 Core Data 中的多个对象保存到 iPodSongs 实体，即当前在 for song in result 中的歌曲标题{}循环.但是我的代码只保存循环中的最后一首歌曲，并且只是不断覆盖同一个对象.每次我都需要创建一个新对象，而不是覆盖同一个对象.我做错了什么?

I'm trying to save multiple objects in Core Data to the IPodSongs entity in a for loop, namely the title of the song currently in the for song in result{} loop. But my code only saves the very last song in the loop, and just keeps overwriting the same object. Instead of overwriting the same object, I need to create a new object each time. What am I doing wrong?

func fetchiPodSongsOnSignup() {

        var appDel: AppDelegate = UIApplication.sharedApplication().delegate as! AppDelegate

        var context: NSManagedObjectContext = appDel.managedObjectContext!

        var newSong = NSEntityDescription.insertNewObjectForEntityForName("IPodSongs", inManagedObjectContext: context) as! NSManagedObject

        var request = NSFetchRequest(entityName: "IPodSongs")

        request.returnsObjectsAsFaults = false

        var results = context.executeFetchRequest(request, error: nil)


        let query = MPMediaQuery.songsQuery()

        let result = query.collections as! [MPMediaItemCollection]

        for song in result {

            for song in song.items as! [MPMediaItem] {

                newSong.setValue("(song.valueForProperty(MPMediaItemPropertyTitle))", forKey: "title")

                println(newSong)

                context.save(nil)

            }
        }

推荐答案

您无需创建将新对象保存到 Core Data 的请求.你做错的是创建一个单一的托管对象，插入它，然后通过循环更改它，而不是为每首歌曲创建一个新对象.

You dont need to create a request to save new objects to Core Data. What you did wrong was create a single managed object, inserted it and then changeded it through the loop instead of creating a new object for each song.

这应该有效:

func fetchiPodSongsOnSignup() {

    var appDel: AppDelegate = UIApplication.sharedApplication().delegate as! AppDelegate

    var context: NSManagedObjectContext = appDel.managedObjectContext!


    let query = MPMediaQuery.songsQuery()

    let result = query.collections as! [MPMediaItemCollection]

    for song in result {

        for song in song.items as! [MPMediaItem] {

            var newSong = NSEntityDescription.insertNewObjectForEntityForName("IPodSongs", inManagedObjectContext: context) as NSManagedObject

            newSong.setValue("(song.valueForProperty(MPMediaItemPropertyTitle))", forKey: "title")

            println(newSong)


        }
    }
    if context.save(&errorPointer == false {
        printlin("Error received while saving")
    }

}

同时把 if context.save(&errorPointer == false {printlin("Error received while Saving")} 放在最后.

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