Core-Data-Stack: NSPersistentContainer einrichten

Überblick über Core Data

import CoreData
// Key classes: NSPersistentContainer, NSManagedObjectContext
// NSManagedObject, NSFetchRequest

NSPersistentContainer erstellen

let container = NSPersistentContainer(name: "MyModel")
container.loadPersistentStores { desc, error in
  if let error { fatalError("Core Data failed: \(error)") }
}

Das Persistence-Controller-Muster

struct PersistenceController {
  static let shared = PersistenceController()
  let container: NSPersistentContainer
  init() {
    container = NSPersistentContainer(name: "MyModel")
    container.loadPersistentStores { _, error in
      if let error { fatalError("\(error)") }
    }
  }
}

viewContext und backgroundContext

let viewCtx = PersistenceController.shared.container.viewContext
let bgCtx = PersistenceController.shared.container.newBackgroundContext()

Managed Objects erstellen

let item = Item(context: viewCtx)
item.timestamp = Date()
try? viewCtx.save()

Objekte abrufen

let request: NSFetchRequest<Item> = Item.fetchRequest()
request.sortDescriptors = [NSSortDescriptor(key: "timestamp", ascending: false)]
let items = try? viewCtx.fetch(request)

Den Kontext speichern

do {
  try viewCtx.save()
} catch {
  print("Save failed: \(error)")
  viewCtx.rollback()
}

SwiftUI-Integration mit @FetchRequest

struct ItemList: View {
  @FetchRequest(
    sortDescriptors: [SortDescriptor(\Item.timestamp, order: .reverse)]
  ) var items: FetchedResults<Item>
  var body: some View {
    List(items) { Text($0.timestamp!.formatted()) }
  }
}

viewContext in SwiftUI injizieren

@main
struct MyApp: App {
  let persistence = PersistenceController.shared
  var body: some Scene {
    WindowGroup {
      ContentView()
        .environment(\.managedObjectContext, persistence.container.viewContext)
    }
  }
}

Objekte löschen

viewCtx.delete(item)
try? viewCtx.save()

In-Memory-Store für Tests

let desc = NSPersistentStoreDescription()
desc.type = NSInMemoryStoreType
container.persistentStoreDescriptions = [desc]
container.loadPersistentStores { _, _ in }

Kurze Überprüfung

Zusammenfassung der Lektion