【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。
标签： arrays swift core-data struct nsdictionary