Core Data vs SwiftData 比較

// Core Data - TodoリストのCRUD
import CoreData
import SwiftUI

// NSManagedObjectのサブクラス
@objc(TodoItem)
class TodoItem: NSManagedObject {
    @NSManaged var id: UUID
    @NSManaged var title: String
    @NSManaged var isCompleted: Bool
    @NSManaged var createdAt: Date
}

// ビューモデル
class TodoViewModel: ObservableObject {
    let container: NSPersistentContainer
    @Published var todos: [TodoItem] = []

    init() {
        container = NSPersistentContainer(name: "TodoModel")
        container.loadPersistentStores { _, error in
            if let error { fatalError("Core Data load failed: \(error)") }
        }
        fetchTodos()
    }

    func fetchTodos() {
        let request = NSFetchRequest<TodoItem>(entityName: "TodoItem")
        request.sortDescriptors = [NSSortDescriptor(key: "createdAt", ascending: false)]
        do {
            todos = try container.viewContext.fetch(request)
        } catch {
            print("Fetch error: \(error)")
        }
    }

    func addTodo(title: String) {
        let todo = TodoItem(context: container.viewContext)
        todo.id = UUID()
        todo.title = title
        todo.isCompleted = false
        todo.createdAt = Date()
        saveContext()
    }

    func toggleTodo(_ todo: TodoItem) {
        todo.isCompleted.toggle()
        saveContext()
    }

    private func saveContext() {
        try? container.viewContext.save()
        fetchTodos()
    }
}

// SwiftData - TodoリストのCRUD
import SwiftData
import SwiftUI

// @Modelマクロ — ボイラープレートなし!
@Model
class TodoItem {
    var id: UUID
    var title: String
    var isCompleted: Bool
    var createdAt: Date

    init(title: String) {
        self.id = UUID()
        self.title = title
        self.isCompleted = false
        self.createdAt = Date()
    }
}

// SwiftUI View — @Queryによる自動更新
struct TodoListView: View {
    @Environment(\.modelContext) private var context
    @Query(sort: \.createdAt, order: .reverse) private var todos: [TodoItem]
    @State private var newTitle = ""

    var body: some View {
        List {
            ForEach(todos) { todo in
                HStack {
                    Image(systemName: todo.isCompleted ? "checkmark.circle.fill" : "circle")
                        .foregroundStyle(todo.isCompleted ? .green : .gray)
                        .onTapGesture { todo.isCompleted.toggle() }
                    Text(todo.title)
                        .strikethrough(todo.isCompleted)
                }
            }
            .onDelete { indexSet in
                indexSet.forEach { context.delete(todos[$0]) }
            }
        }
        .toolbar {
            TextField("新しいTodo...", text: $newTitle)
            Button("追加") {
                guard !newTitle.isEmpty else { return }
                context.insert(TodoItem(title: newTitle))
                newTitle = ""
            }
        }
    }
}