Question

我正在尝试向Core Data添加数据，我认为我已经走上正轨（我对此很新，所以，道歉）从下面的代码中，我的'Aim'是检查Core数据，如果为空则添加默认数据。

代码：

class func musicIsEmpty(managedObjectContext: NSManagedObjectContext)-> Bool{

    let defaultMusic = NSEntityDescription.entityForName("Music", inManagedObjectContext: managedObjectContext)
    let defaultMusicSetOne = NSManagedObject(entity: defaultMusic!, insertIntoManagedObjectContext: managedObjectContext) as? Music
    //defaultMusicSetOne = NSManagedObject(entity: defaultMusic!, insertIntoManagedObjectContext: managedObjectContext) as? Music
    let fetchRequest = NSFetchRequest(entityName: "Music")
    fetchRequest.entity = defaultMusic

    defaultMusicSetOne!.uri = "spotify:track:1puJlKuYGH58SAFgXREUpE"
    defaultMusicSetOne!.duration = 30.0
    defaultMusicSetOne!.starttime = 49.0
    defaultMusicSetOne!.xfade = 10.0
    defaultMusicSetOne!.voiceover = "1.25s Next Up.mp3"

    do{
        if let MusicSetResults =  try managedObjectContext.executeFetchRequest(fetchRequest) as? [NSManagedObject]{

            if MusicSetResults == 0
            {
                defaultMusic!.setValue(defaultMusicSetOne?.uri, forKey: "uri")
                defaultMusic!.setValue(defaultMusicSetOne?.duration, forKey: "duration")
                defaultMusic!.setValue(defaultMusicSetOne?.starttime, forKey: "starttime")
                defaultMusic!.setValue(defaultMusicSetOne?.xfade, forKey: "xfade")
                defaultMusic!.setValue(defaultMusicSetOne?.voiceover, forKey: "voiceover")
                return true
            }

            else
            {
                return false
            }
        }
    }
    catch let error as NSError{
        print("Error: \(error.debugDescription)")
    }
    return false
}

Music.Swift：

extension Music {

@NSManaged var voiceover: String?
@NSManaged var xfade: NSNumber?
@NSManaged var duration: NSNumber?
@NSManaged var starttime: NSNumber?
@NSManaged var uri: String?

}

但是我一直收到错误“这个类不是密钥uri的密钥值编码兼容”我确信这将适用于所有.setValues。我不确定为什么会出现这种情况，因为defaultMusic确实有“uri”字段，而defaultMusic也是音乐对象的实例。 .setValue的格式是错误的吗？还是别的什么？

任何帮助都会很棒！

提前致谢!!

Answer 1

我怀疑你的确是这个意思：

检查实体是否为空，如果是，则插入具有默认值的新对象

class func musicIsEmpty(managedObjectContext: NSManagedObjectContext)-> Bool {

  let musicEntity = NSEntityDescription.entityForName("Music", inManagedObjectContext: managedObjectContext)!      
  let fetchRequest = NSFetchRequest()
  fetchRequest.entity = musicEntity
  do {
    let musicSetResults =  try managedObjectContext.executeFetchRequest(fetchRequest) as! [Music]
    if musicSetResults.isEmpty
    {
      let defaultMusicSetOne = NSManagedObject(entity: musicEntity, insertIntoManagedObjectContext: managedObjectContext) as! Music
      defaultMusicSetOne.uri = "spotify:track:1puJlKuYGH58SAFgXREUpE"
      defaultMusicSetOne.duration = 30.0
      defaultMusicSetOne.starttime = 49.0
      defaultMusicSetOne.xfade = 10.0
      defaultMusicSetOne.voiceover = "1.25s Next Up.mp3"
      return true
    }
  }
  catch let error as NSError{
    print("Error: \(error.debugDescription)")
  }
  return false
}

您也可以考虑保存托管对象上下文以使新对象持久化。

Answer 2

defaultMusic是NSEntityDescription，而不是Music对象。

（有时让Swift使用默认数据类型会让人感到困惑。）

Xcode Swift - 此类不是密钥uri的密钥值编码兼容

2 个答案: