SKILL.md
iOS Data Persistence Skill
Store, sync, and secure data in iOS applications
Learning Objectives
By completing this skill, you will:
- Implement data persistence with SwiftData (iOS 17+)
- Master Core Data for complex data models
- Secure sensitive data with Keychain
- Sync data across devices with CloudKit
Prerequisites
| Requirement | Level |
|---|---|
| iOS Fundamentals | Completed |
| Swift | Intermediate |
Storage Decision Matrix
| Storage Type | Use Case | Encrypted | Synced |
|---|---|---|---|
| UserDefaults | Settings | No | Optional |
| File System | Documents | Optional | Optional |
| Keychain | Secrets | Yes | Optional |
| SwiftData | Structured data | No | Optional |
| Core Data | Complex models | No | Optional |
| CloudKit | Cross-device | Yes | Yes |
Curriculum
Module 1: UserDefaults & AppStorage (2 hours)
Topics:
- UserDefaults basics
- @AppStorage in SwiftUI
- App Groups for sharing
Module 2: SwiftData (iOS 17+) (6 hours)
Topics:
- @Model macro
- ModelContext and @Query
- Relationships and migrations
Module 3: Core Data (6 hours)
Topics:
- NSManagedObject
- NSFetchRequest
- Background contexts
- Migrations
Module 4: Keychain (4 hours)
Topics:
- Keychain Services API
- Biometric access control
- Secure wrapper implementation
Module 5: CloudKit (5 hours)
Topics:
- CKContainer and databases
- CKRecord operations
- Sync strategies
Assessment Criteria
| Criteria | Weight |
|---|---|
| Storage selection | 20% |
| SwiftData/Core Data | 30% |
| Keychain security | 25% |
| CloudKit sync | 25% |
Skill Validation
- Settings Manager: UserDefaults with AppStorage
- Task App: SwiftData with relationships
- Secure Vault: Keychain with biometrics
- Syncing Notes: CloudKit integration