SwiftData

Apple's native persistence framework using @Model classes and declarative queries. Built on Core Data, designed for SwiftUI.

When to Use This Skill

Use this skill when you're:

• Defining @Model classes and relationships
• Writing @Query in SwiftUI views
• Setting up ModelContainer and ModelContext
• Integrating CloudKit sync
• Handling Swift 6 concurrency with @MainActor
• Migrating from Realm or Core Data

Not sure if SwiftData is right? Choose SwiftData for native Apple integration with automatic SwiftUI updates. Use SQLiteData for value types or CloudKit record sharing. Use GRDB for complex raw SQL.

Example Prompts

Questions you can ask Claude that will draw from this skill:

• "I have a notes app with folders. How do I filter notes by folder and sort by last modified with @Query?"
• "When a user deletes a task list, all tasks should auto-delete. How do I set up the relationship?"
• "I'm adding CloudKit sync but get 'Property must have a default value' error. What's wrong?"
• "My app loads 100 tasks with relationships slowly. I think it's N+1 queries. How do I fix this?"
• "We're migrating from Realm to SwiftData. What are the biggest code differences?"
• "How do I handle CloudKit sync conflicts in my chat app?"
• "Which properties should I add indexes to without slowing down writes?"

What's Covered

Core Patterns

• @Model definitions with @Attribute and @Relationship
• @Query with predicates, sorting, and filtering
• ModelContainer setup (SwiftUI app, custom config, in-memory for tests)
• ModelContext operations (insert, fetch, update, delete, batch)

CloudKit Integration

• Enabling sync with ModelConfiguration
• CloudKit constraints (optional/default properties)
• Sync status monitoring and offline handling
• Conflict resolution strategies
• Record sharing (iOS 26+)

Performance

• Prefetching relationships (prevent N+1 queries)
• Batch operations and chunked imports
• Index optimization (iOS 26+)
• Faulting strategies

Swift 6 Concurrency

• @MainActor isolation for models
• Background context patterns with actors
• Safe async/await patterns

Migration Strategies

• Realm → SwiftData pattern equivalents
• Core Data → SwiftData migration
• Dual-stack gradual migration
• CloudKit sync migration from Realm Sync

Key Pattern

Preventing N+1 Queries

// ❌ SLOW: 101 queries (1 + 100 for each album)
let tracks = try modelContext.fetch(FetchDescriptor<Track>())
for track in tracks {
    print(track.album?.title)  // Separate query each time
}

// ✅ FAST: 2 queries total
let descriptor = FetchDescriptor<Track>()
descriptor.relationshipKeyPathsForPrefetching = [\.album]
let tracks = try modelContext.fetch(descriptor)
for track in tracks {
    print(track.album?.title)  // Already loaded
}

Documentation Scope

This page documents the axiom-swiftdata skill—comprehensive SwiftData guidance Claude uses when answering your questions. The skill contains detailed API patterns, code examples, CloudKit configuration, and migration workflows.

For schema migrations: Use database-migration when adding or modifying database columns safely.

Related

• database-migration — Safe schema evolution patterns for adding/modifying columns
• sqlitedata — Alternative using value types (structs) with CloudKit record sharing
• grdb — Raw SQL queries when fine-grained control is needed
• swift-concurrency — @MainActor and actor patterns for Swift 6

Resources

WWDC: 2023-10187, 2023-10195, 2024-10137, 2025-10138

Docs: /swiftdata, /swiftdata/model, /swiftdata/query