Persistence Setup

Persistence Setup Generator

Generates a production-ready persistence layer using SwiftData (iOS 17+) or CoreData with optional iCloud (CloudKit) sync.

When This Skill Activates

• User asks to "add persistence" or "set up data storage"
• User mentions "SwiftData", "CoreData", or "local storage"
• User wants to "sync data to iCloud" or "enable cloud sync"
• User asks about "offline storage" or "data models"

Pre-Generation Checks (CRITICAL)

1. Project Context Detection

Before generating, ALWAYS check:

# Check deployment target
cat Package.swift | grep -i "platform"
# Or check project.pbxproj

# Find existing persistence implementations
rg -l "ModelContainer|NSPersistentContainer|@Model|@Entity" --type swift

# Check for existing SwiftData models
rg "@Model" --type swift | head -5

# Check for CoreData stack
rg "NSManagedObjectContext|NSPersistentStore" --type swift | head -5

# Check existing entitlements for iCloud
cat *.entitlements 2>/dev/null | grep -i "icloud"

2. Framework Selection

Use SwiftData if:

• Deployment target is iOS 17+ / macOS 14+
• User explicitly requests SwiftData
• No existing CoreData implementation

Use CoreData if:

• Deployment target < iOS 17
• Existing CoreData stack present
• User explicitly requests CoreData

3. Conflict Detection

If existing persistence found:

• Ask: Extend existing, migrate to SwiftData, or create separate?

Configuration Questions

Ask user via AskUserQuestion:

1. Framework choice?

   • SwiftData (iOS 17+, recommended)
   • CoreData (older targets)

2. Enable iCloud sync?

   • Yes (requires CloudKit entitlement)
   • No (local only)

3. Generate example model?

   • Yes (with sample Item model)
   • No (just infrastructure)

Generation Process

Step 1: Create Core Files

Always generate:

Sources/Persistence/
├── PersistenceController.swift    # Container setup
├── Repository.swift               # Repository protocol
└── SwiftDataRepository.swift      # Concrete implementation

If example model requested:

Sources/Persistence/Models/
└── Item.swift                     # Sample @Model

If iCloud enabled:

Sources/Persistence/CloudSync/
├── CloudKitConfiguration.swift    # Container identifier
└── SyncStatus.swift               # Sync monitoring

Step 2: Read Templates

Read templates from this skill:

• templates/PersistenceController.swift
• templates/Repository.swift
• templates/SwiftDataRepository.swift
• templates/ExampleModel.swift
• templates/CloudKitConfiguration.swift (if iCloud)
• templates/SyncStatus.swift (if iCloud)

Step 3: Customize for Project

Adapt templates to match:

• Project naming conventions
• Existing model patterns
• Bundle identifier for CloudKit container

Step 4: Integration

Basic Integration:

@main
struct MyApp: App {
    let container = PersistenceController.shared.container

    var body: some Scene {
        WindowGroup {
            ContentView()
                .modelContainer(container)
        }
    }
}

With iCloud sync:

@main
struct MyApp: App {
    let container = PersistenceController.shared.container

    var body: some Scene {
        WindowGroup {
            ContentView()
                .modelContainer(container)
                .environment(\.syncStatus, SyncStatus.shared)
        }
    }
}

iCloud Sync Setup

Required Capabilities (Xcode)

1. iCloud capability:

   • Check "CloudKit"
   • Add container: iCloud.com.yourcompany.yourapp

2. Background Modes (optional, for background sync):

   • Check "Remote notifications"

Required Entitlements

<key>com.apple.developer.icloud-container-identifiers</key>
<array>
    <string>iCloud.com.yourcompany.yourapp</string>
</array>
<key>com.apple.developer.icloud-services</key>
<array>
    <string>CloudKit</string>
</array>

CloudKit Dashboard Setup

1. Go to CloudKit Dashboard
2. Select your container
3. Schema is auto-created from @Model classes
4. Deploy schema to production before release

Generated Code Patterns

Repository Protocol

protocol Repository<T>: Sendable {
    associatedtype T: PersistentModel

    func fetch(predicate: Predicate<T>?, sortBy: [SortDescriptor<T>]) async throws -> [T]
    func insert(_ item: T) async throws
    func delete(_ item: T) async throws
    func save() async throws
}

SwiftData Model

@Model
final class Item {
    var title: String
    var timestamp: Date
    var isCompleted: Bool

    init(title: String, timestamp: Date = .now, isCompleted: Bool = false) {
        self.title = title
        self.timestamp = timestamp
        self.isCompleted = isCompleted
    }
}

Container with CloudKit

let container = try ModelContainer(
    for: Item.self,
    configurations: ModelConfiguration(
        cloudKitDatabase: .private("iCloud.com.yourcompany.yourapp")
    )
)

Verification Checklist

After generation, verify:

• App launches without crashes
• Data persists between app launches
• Models compile without errors
• (If iCloud) CloudKit container exists in dashboard
• (If iCloud) Data syncs between devices
• Repository pattern allows easy testing

Common Customizations

Adding New Models

@Model
final class Project {
    var name: String
    @Relationship(deleteRule: .cascade) var items: [Item]

    init(name: String, items: [Item] = []) {
        self.name = name
        self.items = items
    }
}

// Update container
let container = try ModelContainer(for: Item.self, Project.self)

Custom Fetch Descriptors

let descriptor = FetchDescriptor<Item>(
    predicate: #Predicate { $0.isCompleted == false },
    sortBy: [SortDescriptor(\.timestamp, order: .reverse)]
)
let items = try modelContext.fetch(descriptor)

Migration (SwiftData)

// SwiftData handles lightweight migrations automatically
// For complex migrations, use VersionedSchema

enum ItemSchemaV1: VersionedSchema {
    static var versionIdentifier = Schema.Version(1, 0, 0)
    static var models: [any PersistentModel.Type] { [Item.self] }
}

Troubleshooting

iCloud Sync Not Working

1. Check entitlements match CloudKit container
2. Verify CloudKit Dashboard shows your container
3. Check device is signed into iCloud
4. Deploy schema to production if testing on release build

Data Not Persisting

1. Verify modelContainer modifier is on root view
2. Check save() is called after modifications
3. Look for errors in Console.app

CloudKit Quota Exceeded

• Default quota is generous (free tier: 100MB asset storage)
• Consider pruning old data
• Use cloudKitDatabase: .automatic for shared containers

Related Skills

• networking-layer - For remote API data alongside local cache
• settings-screen - Often uses @AppStorage (simpler persistence)

References

• SwiftData Documentation
• CloudKit Documentation
• Syncing Model Data Across Devices