core-data

Core Data

iOS persistence with Core Data and SwiftData.

Core Data Stack

Basic Setup

// ✅ Core Data stack
class PersistenceController {
    static let shared = PersistenceController()

    let container: NSPersistentContainer

    init(inMemory: Bool = false) {
        container = NSPersistentContainer(name: "DataModel")

        if inMemory {
            container.persistentStoreDescriptions.first?.url = URL(fileURLWithPath: "/dev/null")
        }

        container.loadPersistentStores { description, error in
            if let error = error {
                fatalError("Core Data store failed to load: \(error)")
            }
        }

        container.viewContext.automaticallyMergesChangesFromParent = true
        // Use the NSMergePolicy class properties, not the legacy globals:
        // NSMergeByPropertyObjectTrumpMergePolicy & friends import as mutable
        // globals (`var ...: AnyObject`), which is an error under the Swift 6
        // language mode ("not concurrency-safe … shared mutable state").
        container.viewContext.mergePolicy = NSMergePolicy.mergeByPropertyObjectTrump
    }

    var viewContext: NSManagedObjectContext {
        container.viewContext
    }

    func backgroundContext() -> NSManagedObjectContext {
        container.newBackgroundContext()
    }
}

SwiftUI Integration

// ✅ @FetchRequest in SwiftUI
struct UserListView: View {
    @Environment(\.managedObjectContext) private var viewContext

    @FetchRequest(
        sortDescriptors: [NSSortDescriptor(keyPath: \User.name, ascending: true)],
        animation: .default)
    private var users: FetchedResults<User>

    var body: some View {
        List {
            ForEach(users) { user in
                Text(user.name ?? "Unknown")
            }
            .onDelete(perform: deleteUsers)
        }
    }

    private func deleteUsers(offsets: IndexSet) {
        withAnimation {
            offsets.map { users[$0] }.forEach(viewContext.delete)

            do {
                try viewContext.save()
            } catch {
                print("Failed to save: \(error)")
            }
        }
    }
}