peterbamuhigire/ios-data-persistence

iOS Data Persistence

<!-- dual-compat-start -->

Use When

• iOS data persistence standards with SwiftData as primary local storage and custom API backends for cloud sync. Covers UserDefaults, Keychain, SwiftData (models, queries, relationships, migrations), file storage, offline-first architecture, and...
• The task needs reusable judgment, domain constraints, or a proven workflow rather than ad hoc advice.

Do Not Use When

• The task is unrelated to ios-data-persistence or would be better handled by a more specific companion skill.
• The request only needs a trivial answer and none of this skill's constraints or references materially help.

Required Inputs

• Gather relevant project context, constraints, and the concrete problem to solve; load references only as needed.
• Confirm the desired deliverable: design, code, review, migration plan, audit, or documentation.

Workflow

• Read this SKILL.md first, then load only the referenced deep-dive files that are necessary for the task.
• Apply the ordered guidance, checklists, and decision rules in this skill instead of cherry-picking isolated snippets.
• Produce the deliverable with assumptions, risks, and follow-up work made explicit when they matter.

Quality Standards

• Keep outputs execution-oriented, concise, and aligned with the repository's baseline engineering standards.
• Preserve compatibility with existing project conventions unless the skill explicitly requires a stronger standard.
• Prefer deterministic, reviewable steps over vague advice or tool-specific magic.

Anti-Patterns

• Treating examples as copy-paste truth without checking fit, constraints, or failure modes.
• Loading every reference file by default instead of using progressive disclosure.

Outputs

• A concrete result that fits the task: implementation guidance, review findings, architecture decisions, templates, or generated artifacts.
• Clear assumptions, tradeoffs, or unresolved gaps when the task cannot be completed from available context alone.
• References used, companion skills, or follow-up actions when they materially improve execution.

References

• Use the references/ directory for deep detail after reading the core workflow below.

<!-- dual-compat-end -->

Required Companion Skills

| Skill | When to Apply | |---|---| | ios-swiftdata | Deep SwiftData API — @Attribute, @Relationship, ModelActor, migrations, 10 anti-patterns | | dual-auth-rbac | JWT/refresh-token storage and rotation | | api-pagination | Paginated data fetching with local caching | | vibe-security-skill | Security baseline for all web/API calls | | api-error-handling | Consistent error handling in repository layer |

---

1. Storage Decision Guide

| Data Type | Storage | Example | |---|---|---| | User preferences | UserDefaults | Theme, language, sort order | | Tokens / credentials | Keychain Services | JWT tokens, API keys, passwords | | Structured app data | SwiftData (iOS 17+) | Products, orders, customers | | Large files / images | FileManager | Photos, PDFs, exports | | Temporary cache | URLCache / NSCache | API response caching |

Rule of thumb: simple flag/scalar = UserDefaults. Secret = Keychain. Relationships/querying = SwiftData. Binary blob = FileManager.

---

Additional Guidance

Extended guidance for ios-data-persistence was moved to references/skill-deep-dive.md to keep this entrypoint compact and fast to load.

Use that deep dive for:

• 2. UserDefaults (Simple Preferences Only)
• 3. Keychain Services (Security-Critical Data)
• 4. SwiftData (Primary Local Storage — iOS 17+)
• 5. Repository Pattern (API-Backed Sync)
• 6. Offline-First Architecture
• 7. DTO / Domain Model Mapping
• 8. File Storage (Images, PDFs, Exports)
• 9. iCloud Sync Options
• 10. URLCache / NSCache (Temporary Caching)
• 11. Cross-Skill References
• 12. Anti-Patterns