Swift中的核心数据：只保存for循环中的最后一个对象 [英] Core Data in Swift: Only saving last object in a for loop

问题描述

我试图在Core Data中将多个对象保存到IPodSongs实体中 for 循环中，即当前在 for song in result {} 循环。但是我的代码只保存循环中的最后一首歌，只是不断覆盖同一个对象。而不是覆盖相同的对象，我需要每次创建一个新的对象。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

您不需要创建将新对象保存到Core Data的请求。你做错了是创建一个单一的托管对象，插入它，然后改变它通过循环，而不是为每首歌曲创建一个新的对象。

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.

工作：

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")
    }

}

如果context.save（& errorPointer == false {printlin（保存时收到错误）}} 最后。

Also put if context.save(&errorPointer == false {printlin("Error received while saving")} at the very end.

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