iOS SwiftData

Use When

• Comprehensive SwiftData API reference (iOS 17+) — @Model, @Attribute, @Relationship, ModelContainer, ModelContext, FetchDescriptor, @Query, schema migrations, ModelActor for background work, CloudKit requirements, testing, and 10 anti-patterns. Use alongside ios-data-persistence for offline-first sync engine.
• 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-swiftdata 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.

Evidence Produced

Category	Artifact	Format	Example
Data safety	SwiftData schema migration plan	Markdown doc per skill-composition-standards/references/migration-plan-template.md	docs/ios/swiftdata-migration-2026-04-16.md

References

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

iOS 17+, Swift 5.9+. Primary local storage layer — built on Core Data with modern Swift macros.

Required Companion Skills

Skill	When to Apply
ios-data-persistence	Offline-first sync engine, repository pattern, pending ops queue
ios-development	MVVM architecture, SwiftUI integration, references/concurrency.md

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1. Core 4-Part Architecture

@Model  ──→  ModelContainer  ──→  ModelContext  ──→  View (@Query)
defines          stores              operates          displays

• @Model — Macro that defines a persistent class. Also makes it @Observable.
• ModelContainer — Manages schema + storage config. Sendable — safe across actors.
• ModelContext — In-memory workspace: insert, fetch, delete, save, rollback. NOT Sendable.
• @Query — SwiftUI property wrapper for reactive, always-fresh data. MainActor-bound.

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Additional Guidance

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

Use that deep dive for:

• 2. @Model Macro
• 3. @Attribute Options
• 4. @Relationship
• 5. ModelContainer Setup
• 6. ModelContext Full API
• 7. FetchDescriptor
• 8. @Query
• 9. Schema Migration
• 10. ModelActor (Background Work)
• 11. Testing
• 12. CloudKit Requirements
• 13. Anti-Patterns & Gotchas