arrays - 结构体数组 : How to save in coredata?

Question

我正在尝试将结构数组保存到 coredata 中。我做了很多研究，但找不到解决方案。 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 是我从本教程中得到的解决方案: https://www.youtube.com/watch?v=da6W7wDh0Dw 这并不重要，它只是创建“getContext”函数。 重要的是，在命令行“student.firstName = StudentsStruct.firstName”中，我收到错误“实例成员“firstName”不能在类型 ViewController.StudentStruct 上使用。 经过不断尝试，我已经不知道如何将结构数组放入 coredata 中。

这是数据库 Controller 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)")
            }
        }
    }

}

如有任何帮助，请提前致谢!

好吧，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。现在我得到了 32 个搜索结果。每个条目都是:年龄 = 0；名字 = nil;姓氏 = nil;

作为比较，这段代码在没有循环的情况下也能正常工作:

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")
        }

    }

}

Answer 1

您需要访问item在您的 for 循环中，您当前也正在访问同一对象 Student for 循环中的对象而不是您需要创建一个新的 Student在 for 循环的每次迭代中。

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()