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SwiftData Architecture Expert · rshankras | DecimalAI

codingby rshankras

SwiftData Architecture Expert

rshankras/swiftdata-architecture

Source rshankras/claude-code-apple-skills ↗License MIT

Deep dive into SwiftData design patterns and best practices. Covers schema design, query patterns, repository pattern, and performance optimization.

SkillScore86Maintained

Automatic

Coding pack

Last verified 8/18/2026

What it changes

Passed 19 of 22 test cases with the skill, and 15 of 22 without it.

Without skill68%

With skill86%

Checks it passed that the model alone missed

Configures propertiesToFetch on the FetchDescriptor instance.
Uses the #Unique<UserAccount> macro syntax to specify unique fields.
Specifies macOS 14 or higher as the minimum deployment target requirement.

and 1 more in the full report

5 fixed14 passed either way2 still failing1 broke

Pass-rate lift: +18 pp
Tokens: +25%
Agent turns: 0%
Response time: -22%

Model gemini-3.6-flashMeasured 8/18/2026v119 of 22 cases passed with skill

Tokens, turns and time describe resource use, not a dollar price.

Use this skill

Save it into your project's skills folder. Claude Code picks it up in its next session.

curl -fsSL --create-dirs -o .claude/skills/rshankras-swiftdata-architecture/SKILL.md https://app.decimal.ai/s/rshankras-swiftdata-architecture/SKILL.md

Want it pinned and updatable? pip install "decimalai>=0.15", then decimalai skills add rshankras-swiftdata-architecture, and start Claude Code with claude --plugin-dir "$(git rev-parse --show-toplevel)/.agents"

1 · One-time — install the CLI (docs ↗)

pip install "decimalai>=0.15"

2 · Get the skill — writes .agents/skills/rshankras-swiftdata-architecture/ and pins it in .decimal/skills.lock

decimalai skills add rshankras-swiftdata-architecture

No CLI? Get the same file — curl · raw file

curl -fsSL --create-dirs -o .claude/skills/rshankras-swiftdata-architecture/SKILL.md https://app.decimal.ai/s/rshankras-swiftdata-architecture/SKILL.md

Raw file: /s/rshankras-swiftdata-architecture/SKILL.md ↗ · machine-readable summary at /s/rshankras-swiftdata-architecture.json ↗

Safety checks: 3 of 3 passed

Code scan CleanIntent PassedContent Clean

See it in action

One of 5 test cases the skill fixed. Same model, same prompt, with and without the skill.

1 of 5

Prompt

I am defining a SwiftData @Model for UserAccount in my macOS app. I need to guarantee that the user's account ID remains strictly unique across imports. How should I write this constraint in the model declaration?

What was checked, without and with the skill
Checked	Without skill	With skill
Uses the #Unique<UserAccount> macro syntax to specify unique fields.	Missed	Passed

case-04 · gemini-3.6-flash · 8/18/2026 · answers are capped and redacted

What's inside

The instructions your model reads when the skill loads.

SKILL.md136 linessingle file

SwiftData Architecture Expert

You are a macOS development expert specializing in SwiftData persistence. You help developers design efficient data models, write performant queries, and build testable data layers.

Your Role

Guide developers through SwiftData architecture decisions, from schema design to query optimization to data layer abstraction. Focus on patterns that work well with SwiftUI and modern Swift concurrency.

Core Focus Areas

Schema Design - @Model classes, relationships, attributes, unique constraints
Query Patterns - @Query, FetchDescriptor, predicates, sorting, pagination
Repository Pattern - Protocol-based data abstraction, dependency injection, testing
Performance - Batch operations, background contexts, lazy loading, memory management

When This Skill Activates

Designing data models for a new app
Migrating from Core Data to SwiftData
Optimizing slow queries or high memory usage
Building a testable data layer
Reviewing SwiftData usage patterns

Quick Decision Guide

Question	Answer
Should I use SwiftData or Core Data?	SwiftData for new projects
@Query or FetchDescriptor?	@Query in views, FetchDescriptor in services
Should I use a repository pattern?	Yes, if you need testability or data source flexibility
How to handle large datasets?	Pagination + background context + batch operations
Relationships: optional or required?	Default to optional unless the model is invalid without it

Common Pitfalls

1. Missing Unique Constraints

// Wrong - duplicate entries on re-import
@Model class Contact {
    var email: String

Track record

Benchmark

19 / 22

test cases passed, vs 15 / 22 without

Adoption

Users: 0
Times used: 0

Safety and source details

SkillSafety

✓ 3 of 3 passed

Code scan15 of 15 checks clean

0 critical · 0 warning · 0 info — scanner v4 — 8/3/2026

View 15 scanner checks

live_secretremote_code_executionreverse_shelldata_exfiltrationssrf_metadataagent_snoopinganti_refusaldestructive_commandsobfuscated_unicodeunicode_homoglyphopaque_blobsuspicious_urltool_overreachtrigger_abuseprompt_injection_phrasing

IntentSafe

LLM judge · does the skill do what it claims

ContentClean

LLM judge · policy & harmful-content review

Source

Imported

rshankras / claude-code-apple-skills

skills/macos/swiftdata-architecture/SKILL.md

View on GitHub ↗

License MITImported 8/3/2026Version v1

More skills from the same source and nearby in the registry, with their headline benchmark lift.

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See it in action

What's inside

SwiftData Architecture Expert

Your Role

Core Focus Areas

When This Skill Activates

Quick Decision Guide

Common Pitfalls

1. Missing Unique Constraints

Track record

Benchmark

Adoption

SkillSafety

Source

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