结构数组：如何保存在 coredata 中？
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【中文标题】结构数组：如何保存在 coredata 中？【英文标题】：Array of structs: How to save in coredata? 【发布时间】：2017-06-14 12:09:03 【问题描述】：我正在尝试将结构数组保存到 coredata 中。我做了很多研究，但我找不到解决方案。 这是我得到的：
import Cocoa
import CoreData
class ViewController: NSViewController
struct StudentsStruct
let firstName: String
let lastName: String
let age: Int
let Studentsdata: [StudentsStruct] = [StudentsStruct(firstName: "Albert", lastName: "Miller", age: 24), StudentsStruct(firstName: "Susan", lastName: "Gordon", age: 24), StudentsStruct(firstName: "Henry", lastName: "Colbert", age: 24)]
override func viewDidLoad()
super.viewDidLoad()
let student: Student = NSEntityDescription.insertNewObject(forEntityName: "Student", into: DatabaseController.getContext()) as! Student
for items in Studentsdata
student.firstName = StudentsStruct.firstName
student.lastName = StudentsStruct.lastName
student.age = StudentsStruct.age
DatabaseController.saveContext()
let fetchRequest: NSFetchRequest<Student> = Student.fetchRequest()
print (student)
DatabaseController 是我从本教程中获得的解决方案： https://www.youtube.com/watch?v=da6W7wDh0Dw 它不是那么重要，它只是制作“getContext”功能。 重要的是，在命令行“student.firstName = StudentsStruct.firstName”中，我收到错误“实例成员“firstName”不能用于 ViewController.StudentStruct 类型。 在尝试和尝试之后，我已经没有如何将结构数组放入 coredata 的想法了。
这是 DatabaseController 文件：
import Foundation
import CoreData
class DatabaseController
private init()
class func getContext() -> NSManagedObjectContext
return DatabaseController.persistentContainer.viewContext
// MARK: - Core Data stack
static var persistentContainer: NSPersistentContainer =
let container = NSPersistentContainer(name: "StudentCoreFile")
container.loadPersistentStores(completionHandler: (storeDescription, error) in
if let error = error
fatalError("Unresolved error \(error)")
)
return container
()
class func saveContext ()
let context = DatabaseController.persistentContainer.viewContext
if context.hasChanges
do
try context.save()
catch
// Replace this implementation with code to handle the error appropriately.
// fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
let nserror = error as NSError
fatalError("Unresolved error \(nserror), \(nserror.userInfo)")
在此先感谢您的帮助！
好的，你是对的，我忘了执行 fetchrequest。这是我当前的代码：
import Cocoa
import CoreData
class ViewController: NSViewController
struct StudentsStruct
let firstName: String
let lastName: String
let age: Int
let Studentsdata: [StudentsStruct] = [StudentsStruct(firstName: "Albert", lastName: "Miller", age: 24), StudentsStruct(firstName: "Susan", lastName: "Gordon", age: 24), StudentsStruct(firstName: "Henry", lastName: "Colbert", age: 24)]
override func viewDidLoad()
super.viewDidLoad()
let student: Student = NSEntityDescription.insertNewObject(forEntityName: "Student", into: DatabaseController.getContext()) as! Student
for item in Studentsdata
let student: Student = NSEntityDescription.insertNewObject(forEntityName: "Student", into: DatabaseController.getContext()) as! Student
student.firstName = item.firstName
student.lastName = item.lastName
student.age = Int16(item.age)
DatabaseController.saveContext()
let fetchRequest: NSFetchRequest<Student> = Student.fetchRequest()
do
let searchResults = try DatabaseController.getContext().fetch(fetchRequest)
print("number of results: \(searchResults.count)")
for result in searchResults as [Student]
print(student)
catch
print ("error")
它运行没有错误。现在我得到 32 个搜索结果。每个条目是：age = 0;名字 = 无；姓氏 = 无；
为了比较，这段代码，没有循环是有效的：
import Cocoa
import CoreData
class ViewController: NSViewController
override func viewDidLoad()
super.viewDidLoad()
let student: Student = NSEntityDescription.insertNewObject(forEntityName: "Student", into: DatabaseController.getContext()) as! Student
student.firstName = "henry"
student.lastName = "miller"
student.age = 22
DatabaseController.saveContext()
let fetchRequest: NSFetchRequest<Student> = Student.fetchRequest()
do
let searchResults = try DatabaseController.getContext().fetch(fetchRequest)
print("number of results: \(searchResults.count)")
for result in searchResults as [Student]
print(student)
catch
print ("error")
【问题讨论】：
您如何从数组Studentsdata 获得 32 个对象，只有 3 个对象
我不知道。每次我调用该函数时，ißm 都会再获得 4 个搜索结果。 （现年 48 岁）。
Studentdata 中的循环似乎有效，我可以在控制台中看到。问题应该在 fetchrequest 中。
我添加了一个较小版本的代码，它正在工作。这很奇怪，因为从 fetchrequest 开始就一样了。
【参考方案1】：
您需要在 for 循环中访问 item 并且您当前正在 for 循环中访问相同的对象 Student 对象，而不是您需要在 for 循环的每次迭代中创建一个新的 Student。
for item in Studentsdata
//Create new student in for loop
let student = NSEntityDescription.insertNewObject(forEntityName: "Student", into: DatabaseController.getContext()) as! Student
//To get firstName, lastName and age access the item
student.firstName = item.firstName
student.lastName = item.lastName
student.age = item.age
//Save context now
DatabaseController.saveContext()
【讨论】：
谢谢，看起来不错。建筑物运行没有错误。但是当我打印出“学生”时，数据仍然是空的。 （实体：学生；id：0x340000bfetchRequest 调用fetch
不确定您是否从上面获取我的 cmets：我添加了当前代码。也用于比较正在运行的较小版本。在控制台中，“for-in”功能似乎有效。之后，可能 fetchrequest 不起作用。奇怪，因为它在较小的“工作版本”中是一样的。谢谢【参考方案2】：
如果有人感兴趣，我找到了解决方案： 您首先必须像这样在 CoredataEntity 类中设置结构：
import Foundation
import CoreData
struct StudentsStruct
let firstName: String
let lastName: String
let age: Int
@objc(Student)
public class Student: NSManagedObject
@NSManaged public var firstName: String?
@NSManaged public var lastName: String?
@NSManaged public var age: Int16
var allAtributes : StudentsStruct
get
return StudentsStruct(firstName: self.firstName!, lastName: self.lastName!, age: Int(self.age))
set
self.firstName = newValue.firstName
self.lastName = newValue.lastName
self.age = Int16(newValue.age)
然后使用相同的结构粘贴数据：
import Cocoa
import CoreData
class ViewController: NSViewController
let studentsdata: [StudentsStruct] = [StudentsStruct(firstName: "Albert", lastName: "Miller", age: 24), StudentsStruct(firstName: "Susan", lastName: "Gordon", age: 24), StudentsStruct(firstName: "Henry", lastName: "Colbert", age: 24)]
override func viewDidLoad()
super.viewDidLoad()
for items in studentsdata
let student: Student = NSEntityDescription.insertNewObject(forEntityName: "Student", into: DatabaseController.getContext()) as! Student
student.allAtributes = items
DatabaseController.saveContext()
let fetchRequest: NSFetchRequest<Student> = Student.fetchRequest()
do
let searchResults = try DatabaseController.getContext().fetch(fetchRequest)
print("number of results: \(searchResults.count)")
for result in searchResults as [Student]
print("student: \(firstName), \(lastName), \(age)" )
catch
print ("error: \(error)")
就是这样。
【讨论】：
这是不需要的，您可以在不需要的任何地方声明结构，例如该结构应该在 coredata 类中，如果您不在该类中声明它，您仍然可以在该类中使用结构。 【参考方案3】：也许这是懒惰。您也可以将您的数组编码为 json 对象，然后在您的 NSManagedObject 上为其创建一个可转换的字段。当您想要检索时，您只需解码并向下转换为正确的类型。这就是我在我的一个项目中所做的；工作正常。
【讨论】：
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