Why SwiftData

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Goal

Understand why local persistence matters and how SwiftData compares to Core Data, then add a local "favorite" feature to the intermediate list app.

Prerequisites

• Intermediate MVVM list app (URLSession + async/await)

The persistence gap

The intermediate app fetches data from a public API every launch. This means:

• No offline access — the screen is blank without network.
• Slow start — users stare at a spinner before seeing content.
• No user data — bookmarks, favorites, or notes can't be saved.

Local persistence fixes all three. You cache API results and store user-created data in a database on the device.

SwiftData vs Core Data

Feature	Core Data	SwiftData
API style	Objective-C heritage, NSManagedObject	Swift-native with @Model macro
Boilerplate	NSPersistentContainer, entity descriptions, codegen	ModelContainer + @Model — zero config
Concurrency	Manual viewContext / performBackgroundTask	@MainActor by default, ModelActor for background
Observable	@ObservedObject for fetch results	@Query auto-refreshes the view
Migration	Lightweight + heavy (versioning)	Automatic lightweight

SwiftData is not a wrapper around Core Data — it's a separate framework built on the same SQLite storage engine, but with a modern Swift-first API.

Plan for this tier

Over the next pages you will:

1. Add SwiftData to the project (this page)
2. Create @Model classes for cached items and user favorites
3. Replace the intermediate @ObservableObject ViewModel with a SwiftData-backed one
4. Favorites persist across launches and sync with the list view

Add SwiftData to the project

In your intermediate Xcode project, add the import:

import SwiftData

Every SwiftData app needs a ModelContainer in the app entry point:

import SwiftUI
import SwiftData

@main
struct ListApp: App {
    var body: some Scene {
        WindowGroup {
            ContentView()
        }
        .modelContainer(for: [CachedItem.self])
    }
}

The .modelContainer modifier creates the container and injects it into the environment. The CachedItem model is defined next.

Next: Add SwiftData — define @Model classes and build a CRUD ViewModel.