Array of structs: How to save in coredata? - arrays

Question

I´m trying to save an array of structs into coredata. I did a lot of research, but i cannot find the solution.
Here´s what i´ve got:
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)
}
}
The DatabaseController is solution i´ve got from this tutorial:
https://www.youtube.com/watch?v=da6W7wDh0Dw
It´s not so important, it´s just making the "getContext" function.
Whats important, in teh commandline "student.firstName = StudentsStruct.firstName" i´m getting the error "instance member "firstName" cannot be used on type ViewController.StudentStruct.
After trying and trying, i´m running out of ideas how to get the array of structs into coredata.
This is the DatabaseController file:
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)")
}
}
}
}
for any help thanks in advance!
Ok, you are right, i forgot to execute the fetchrequest. Here´s my current code:
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")
}
}
}
It´s running without errors. Now i´m getting 32 search results. Every entry is: age = 0; firstName = nil; lastName = nil;
For comparison, this code, without the loop is working:
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

You need to access the item in your for loop also you are currently accessing the same object Student object in for loop instead of that you need to create a new Student in every iteration of for loop.
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()

Answer 2

In case someone is interested, I found the solution:
You first have to set up the struct in the CoredataEntity Class like that:
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)
}
}
}
Then use the same struct to paste the data:
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)")
}
}
}
Thats it.

Answer 3

Perhaps this is lazy. You could also just encode your array as a json object and then create a field on your NSManagedObject for it as a transformable. When you want to retrieve you'd just decode and downcast to the proper type. That's what I did in one of my projects; worked fine.