CoreData - 獲取代碼swift3

Question

以下不起作用拋出一個錯誤，請幫助如何編寫從用戶實體獲取數據的代碼。

附屏幕enter image description here

Answer 1

抓住appDelegate對象和context

let appDelegate = UIApplication.shared.delegate as! AppDelegate 
let context = appDelegate.persistentContainer.viewContext 

在覈心數據添加記錄

let user = NSEntityDescription.insertNewObject(forEntityName: "UsersClass", into: context) as! UsersClass 
user.userName = "Rajan" 
appDelegate.saveContext() 

擷取

let fetchRequest:NSFetchRequest<UsersClass> = UsersClass.fetchRequest() 

然後執行這個請求

do { 
    let searchResults = try context.fetch(fetchRequest) 
    for trans in searchResults { 
     print(trans.username!) 
    } 
} 
catch { 
    //Handle error 
} 

UsersClass + CoreDataProperties.swift

import Foundation 
import CoreData 

extension UsersClass { 

    @nonobjc public class func fetchRequest() -> NSFetchRequest<UsersClass> { 
     return NSFetchRequest<UsersClass>(entityName: "UsersClass"); 
    } 

    @NSManaged public var userName: String? 

} 

這裏是我提出的Sample。