获取零核心数据对象返回错误

Question

我的应用程序仍处于开发阶段，我正在尝试注册用户。我想检查核心数据中是否有现有用户，如果结果返回0，那么我将添加一个新用户。如果没有，我将更新从服务器端获取的现有用户。我也知道目前，我的核心数据是空。但是，当我尝试获取数据时，在

行

let searchResult = try managedContext.fetch(fetchRequest) as! [User]

它转到catch语句并打印错误。

  

错误Domain = Foundation._GenericObjCError Code = 0＆＃34;（null）＆＃34;

以下是我的代码。尝试在Google上搜索确切的错误代码，但我找不到任何错误代码。

func SaveToCoreData(){
    guard let appDelegate = UIApplication.shared.delegate as? AppDelegate else {
        return
    }
    let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "User")
    let managedContext = appDelegate.persistentContainer.viewContext

    do{
        let searchResult = try managedContext.fetch(fetchRequest) as! [User]
        let entity = NSEntityDescription.entity(forEntityName: "User", in: managedContext)
        let newUser = NSManagedObject(entity: entity!, insertInto: managedContext)

        if(searchResult.count == 0){
            newUser.setValue(emailField, forKey: "email")
            newUser.setValue(jsonReply["profilePicture"].stringValue, forKey: "profilePicture")

            do{
                try managedContext.save()
            } catch let error as NSError{
                ShowAlert(title: "", message: error.description)
            }
        }
        else if(searchResult.count == 1){
            let updateUser = user[0]

            updateUser.setValue(emailField, forKey: "email")
            updateUser.setValue(jsonReply["profilePicture"].stringValue, forKey: "profilePicture")

            do{
                try managedContext.save()
                self.ShowTabBar()
            } catch let error as NSError{
                ShowAlert(title: "", message: error.description)
            }
        }

    } catch let error as NSError{
        print(error)
    }

}