Local Storage (SwiftData)

Relax. We'll talk through this in plain words — no textbook voice.

What you'll walk away with

Understand Local Storage (SwiftData) with nothing to be intimidated by
Get comfortable running Xcode/SwiftUI code yourself
Be able to apply this concept in a real project right away

Let's think about it this way for a second

SwiftData is a framework that modernizes Core Data (Apple's traditional local database framework) with Swift-native syntax — just adding the `@Model` macro to a class (a concept similar to Android's Room `@Entity`) auto-generates a database table, no manual SQL/DAO required. Using the `@Query` property wrapper in a View automatically fetches/observes data from the database — when data changes, the UI automatically updates too (similar to Room's Flow concept).

Let's connect this to a real-world scenario

If you define `@Model class TodoItem { var title: String; var isDone: Bool; init(title: String, isDone: Bool = false) { self.title = title; self.isDone = isDone } }` and write `@Query private var todos: [TodoItem]` in your View — all the todo items in the database get automatically fetched, and calling `modelContext.insert(newTodo)` permanently saves data to the device disk, so it'll still be there even after force-closing and reopening the app.

SwiftData = Apple's modern, type-safe local database framework (a modernization of Core Data)
@Model macro = auto-generates a class as a database table (similar to Room's @Entity)
@Query = automatically fetches/observes database data inside a View (similar to Room's Flow)

Let's look at it together

swift

import SwiftData

@Model
class TodoItem {
    var title: String
    var isDone: Bool

    init(title: String, isDone: Bool = false) {
        self.title = title
        self.isDone = isDone
    }
}

struct TodoListScreen: View {
    @Environment(\.modelContext) private var modelContext
    @Query private var todos: [TodoItem]

    var body: some View {
        List(todos) { todo in Text(todo.title) }
    }
}

You should see

Even after force-closing the app and reopening it, the todo list data doesn't disappear and stays intact (thanks to SwiftData pulling it back).

5-minute try-it

Write `TodoItem` (@Model) yourself and display it using `@Query` inside `TodoListScreen` — add a new item with `modelContext.insert()`, then confirm the data still remains after force-closing/reopening the app.

A quick heads-up

If you change your `@Model` schema (properties) during an app update without a migration strategy in place, it can cause data compatibility issues for existing users — the same kind of risk as Room's version/Migration concept.

Easy traps

Confusing `@Model` class with `Codable` (from the URLSession lesson) — `@Model` is for local database persistence, while `Codable` is for JSON encoding/decoding; they serve different purposes
Forgetting `try modelContext.save()` after calling `modelContext.insert()` (unless auto-save is enabled) — data might not get permanently saved to disk

Now try it yourself

You'll know it worked when: Even after force-closing the app and reopening it, the todo list data doesn't disappear and stays intact (thanks to SwiftData pulling it back).