CoreData - 获取代码 swift3

Question

下面不工作抛出错误，请帮助如何编写代码以从用户实体中获取数据。

附屏enter image description here

Answer 1

抓取appDelegate 对象和context

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

在 Core Data 中添加记录

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

正在抓取

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

然后执行这个请求

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?

}

这是我制作的Sample。