Storage Patterns

Use this guide when implementing or modifying data persistence.

Default: In-Memory with Sample Data

Unless explicitly requested, use in-memory data with rich dummy data:

In-Memory Models (Default)

struct Note: Identifiable {
    let id: UUID
    var title: String
    var content: String

    init(title: String, content: String = "") {
        self.id = UUID()
        self.title = title
        self.content = content
    }

    static let sampleData: [Note] = [
        Note(title: "Meeting Notes", content: "Discuss Q2 roadmap"),
        Note(title: "Recipe", content: "Eggs, pecorino, guanciale"),
    ]
}

In-Memory ViewModel (Default)

@Observable @MainActor
class NotesViewModel {
    var notes: [Note] = Note.sampleData

    func addNote(title: String) {
        notes.insert(Note(title: title), at: 0)
    }

    func deleteNote(_ note: Note) {
        notes.removeAll { $0.id == note.id }
    }
}

@AppStorage

@AppStorage("sortOrder") private var sortOrder = "date"
@AppStorage("showCompleted") private var showCompleted = true

SwiftData (ONLY when user explicitly requests persistence)

Use @Model, @Query, .modelContainer ONLY if user says "save", "persist", "database", or "SwiftData":

import SwiftData

@Model
class Note {
    var title: String
    var content: String
    var createdAt: Date

    init(title: String, content: String = "") {
        self.title = title
        self.content = content
        self.createdAt = Date()
    }
}

App entry with container:

@main
struct MyApp: App {
    var body: some Scene {
        WindowGroup { ContentView() }
        .modelContainer(for: Note.self)
    }
}