从CoreData模块获取数据

Question

我正在Swift 3.0中的一个项目上工作，我有一个CoreData模块，该模块具有五个属性，类型为String，名称为NSManageObject名称为MP3Details 。 它们分别是duration， trackID ， trackName ， trackURL 。

要求是，一旦我通过trackID ，就需要检索与该ID相关的元素。 例如，一旦我通过trackID我就应该获得属于该轨道ID的轨道持续时间， trackName等。

到目前为止，我得到的是一个空数组。 我传递trackID并获取的信息的部分完成的代码属于该ID，如下所示。 我在这里想念什么？

我传递trackID

if let arr = StorageManager.getTrackId(playlistName: playlistName) {
    for object in arr {
        let trackId = object.trackID
        print(trackId ?? "ID")

        if let detailsArr = StorageManager.getTrackDetails(trackId: trackId) {
           print("CoreDataItemArray :", detailsArr)

        }
    }

是否从CoreData请求详细信息的方法

public static func getTrackDetails(trackId:String?) -> [MP3Details]?{
    let appDelegate = UIApplication.shared.delegate as! AppDelegate;
    let context = appDelegate.persistentContainer.viewContext;

    let request = NSFetchRequest<NSFetchRequestResult>(entityName: MP3_DETAILS_ENTITY)
    if(trackId != nil){
        request.predicate = NSPredicate(format:"trackID = %@", trackId!)
    }
    request.returnsObjectsAsFaults = false

    do{
        let results = try context.fetch(request)
        print("Result : ",results)
        if(results.count > 0 ){

            return results as? [MP3Details]
        }else{
            print("No Mp3 results for the track ID")
        }

    }catch{
        print("Error in fetching items")
    }
    return nil;
}

Answer 1

func loadData（）->无效{

    guard let appDelegate = UIApplication.shared.delegate as? AppDelegate else {
        return
    }

    let managedObjContext = appDelegate.persistentContainer.viewContext
    let fetchRequest = NSFetchRequest<NSManagedObject>(entityName: "Person")
    do {
        names = try managedObjContext.fetch(fetchRequest)
    } catch let error as NSError {
        print("Error while fetching the data:: ",error.description)
    }

}

@IBAction func addNewName(_ sender: Any) {
    let alert = UIAlertController(title: "Add Name", message: "Add new name:", preferredStyle: UIAlertControllerStyle.alert)
    let alertAction = UIAlertAction(title: "Add", style: UIAlertActionStyle.default) { action in

        guard let textField = alert.textFields?.first ,
            let nameToSave = textField.text else{
                return
        }
        print("nameToSave::: ",nameToSave)
        self.save(name:nameToSave)
        self.hitListTableView.reloadData()
    }
    alert.addTextField()

    let alertCancelAction = UIAlertAction(title: "Cancel", style: UIAlertActionStyle.cancel, handler: nil)

    alert.addAction(alertAction)
    alert.addAction(alertCancelAction)

    self.present(alert, animated: true, completion: nil)

}

func save(name:String) -> Void {

    guard let appDelegate = UIApplication.shared.delegate as? AppDelegate else {
        return
    }
    let managedContext = appDelegate.persistentContainer.viewContext
    let entity = NSEntityDescription.entity(forEntityName: "Person", in: managedContext)
    let person = NSManagedObject(entity: entity!, insertInto: managedContext)
    person.setValue(name, forKey: "name")

    do {
        try managedContext.save()
        names.append(person)
    } catch let error as NSError {
        print("Error while saving the data: ",error.localizedDescription)
    }
}

Answer 2

尝试将谓词行替换为：

request.predicate = NSPredicate(format:"%K == %@", "trackID", trackId!)