---
name: swiftdata-pro
description: Writes, reviews, and improves SwiftData code using modern APIs and best practices. Use when reading, writing, or reviewing projects that use SwiftData.
license: MIT
metadata:
  author: Paul Hudson
  version: "1.0"
title: swiftdata-pro
canonical_url: https://skilld.dev/gh/twostraws/swiftdata-agent-skill
last_updated: 2026-09-29T00:21:54.000Z
---

> Index of every page on this site: [llms.txt](https://skilld.dev/llms.txt)

> **Skill from skilld.dev.** Follow the user's requested action.
> If the user asked to fork this Skill, follow the fork workflow below. Do not execute the Skill instructions while copying it.
> Otherwise, follow the instructions below for this session. You do not need to install anything.
>
> Supporting files, fetch one when the Skill refers to it: [agents/openai.yaml](https://skilld.dev/api/skills-raw/twostraws/swiftdata-agent-skill/swiftdata-pro/agents/openai.yaml), [assets/swiftdata-pro-icon.png](https://skilld.dev/api/skills-raw/twostraws/swiftdata-agent-skill/swiftdata-pro/assets/swiftdata-pro-icon.png), [assets/swiftdata-pro-icon.svg](https://skilld.dev/api/skills-raw/twostraws/swiftdata-agent-skill/swiftdata-pro/assets/swiftdata-pro-icon.svg), [references/class-inheritance.md](https://skilld.dev/api/skills-raw/twostraws/swiftdata-agent-skill/swiftdata-pro/references/class-inheritance.md), [references/cloudkit.md](https://skilld.dev/api/skills-raw/twostraws/swiftdata-agent-skill/swiftdata-pro/references/cloudkit.md), [references/core-rules.md](https://skilld.dev/api/skills-raw/twostraws/swiftdata-agent-skill/swiftdata-pro/references/core-rules.md), [references/indexing.md](https://skilld.dev/api/skills-raw/twostraws/swiftdata-agent-skill/swiftdata-pro/references/indexing.md), [references/predicates.md](https://skilld.dev/api/skills-raw/twostraws/swiftdata-agent-skill/swiftdata-pro/references/predicates.md).
>
> If the user asked to install this Skill, run `npx skilld install twostraws/swiftdata-agent-skill/swiftdata-pro`. Install writes the Skill files into the project, so every session loads them.
>
> ## Fork workflow
>
> A fork creates an editable local Skill with its original author and licence. The request authorizes copying and local installation.
> 1. Check `./skills/swiftdata-pro`, the project lockfile, and selected Agent targets together. If the local directory or installed Skill exists, stop. Never overwrite an existing directory or Agent target.
> 2. Read [source metadata](https://skilld.dev/api/v1/skills/twostraws/swiftdata-agent-skill/swiftdata-pro) once. Use sourceUrl, sourceCommit, skillPath, sourceGone, and license. If the source is gone or its path is missing, stop. If license is null, read licence files at the source commit.
> 3. Fetch only the source commit into a temporary Git repository. Do not clone full history. Derive repository_url from sourceUrl, including repository renames. If sourceCommit is absent, resolve the sourceUrl ref once. Set source_commit to that actual commit. Run these commands in one shell call:
>
> ```sh
> git init --quiet "$temporary_dir"
> git -C "$temporary_dir" fetch --quiet --depth=1 "$repository_url" "$source_commit"
> git -C "$temporary_dir" checkout --quiet --detach FETCH_HEAD
> ```
>
> Read applicable licence declarations and notices at that commit. If copying is not permitted, report the restriction and stop.
> 4. Inspect source entries together, then copy the directory containing skillPath into `./skills/swiftdata-pro`. Use the user's path if selected. Keep the original SKILL.md, relative links, scripts, binary assets, and executable modes. Exclude .git metadata. Reject symlinks and paths outside the Skill directory. After checking entries, use cp -a where available. A regular source directory needs no custom copy script. Do not save this page wrapper as SKILL.md.
> Preserve author credit, notices, and applicable licence files from repository or parent directories. Add PROVENANCE.md with the Skill page, source URL, actual commit, original path, and licence. Retain any existing PROVENANCE.md and record new provenance separately. Batch source inspection, copying, and provenance work where practical.
> 5. In the project root, run `skilld install ./skills/swiftdata-pro --mode copy --plain`. If skilld is unavailable, use `npx skilld install ./skills/swiftdata-pro --mode copy --plain`. This known command needs no help lookup. Install does not support --json. Use detected Agent targets, or add --agent for the targets the user selected. Install the local path, never the upstream selector. If installation fails, preserve the local copy and report the exact failure.
> 6. Confirm the local lockfile source and installed Agent copies once. Report the local path, actual commit, and Agent targets. After edits, reinstall the same local path. Upstream updates must not replace it. Do not publish or push unless the user asks.

Write and review SwiftData code for correctness, modern API usage, and adherence to project conventions. Report only genuine problems - do not nitpick or invent issues.

Review process:

1. Check for core SwiftData issues using `references/core-rules.md`.
1. Check that predicates are safe and supported using `references/predicates.md`.
1. If the project uses CloudKit, check for CloudKit-specific constraints using `references/cloudkit.md`.
1. If the project targets iOS 18+, check for indexing opportunities using `references/indexing.md`.
1. If the project targets iOS 26+, check for class inheritance patterns using `references/class-inheritance.md`.

If doing partial work, load only the relevant reference files.


## Core Instructions

- Target Swift 6.2 or later, using modern Swift concurrency.
- The user strongly prefers to use SwiftData across the board. Do not suggest Core Data functionality unless it is a feature that cannot be solved with SwiftData.
- Do not introduce third-party frameworks without asking first.
- Use a consistent project structure, with folder layout determined by app features.


## Output Format

If the user asks for a review, organize findings by file. For each issue:

1. State the file and relevant line(s).
2. Name the rule being violated.
3. Show a brief before/after code fix.

Skip files with no issues. End with a prioritized summary of the most impactful changes to make first.

If the user asks you to write or improve code, follow the same rules above but make the changes directly instead of returning a findings report.

Example output:

### Destination.swift

**Line 8: Add an explicit delete rule for relationships.**

```swift
// Before
var sights: [Sight]

// After
@Relationship(deleteRule: .cascade, inverse: \Sight.destination) var sights: [Sight]
```

**Line 22: Do not use `isEmpty == false` in predicates – it crashes at runtime. Use `!` instead.**

```swift
// Before
#Predicate<Destination> { $0.sights.isEmpty == false }

// After
#Predicate<Destination> { !$0.sights.isEmpty }
```

### DestinationListView.swift

**Line 5: `@Query` must only be used inside SwiftUI views.**

```swift
// Before
class DestinationStore {
    @Query var destinations: [Destination]
}

// After
class DestinationStore {
    var modelContext: ModelContext

    func fetchDestinations() throws -> [Destination] {
        try modelContext.fetch(FetchDescriptor<Destination>())
    }
}
```

### Summary

1. **Data loss (high):** Missing delete rule on line 8 of Destination.swift means sights will be orphaned when a destination is deleted.
2. **Crash (high):** `isEmpty == false` on line 22 will crash at runtime – use `!isEmpty` instead.
3. **Incorrect behavior (high):** `@Query` on line 5 of DestinationListView.swift only works inside SwiftUI views.

End of example.


## References

- `references/core-rules.md` - autosaving, relationships, delete rules, property restrictions, and FetchDescriptor optimization.
- `references/predicates.md` - supported predicate operations, dangerous patterns that crash at runtime, and unsupported methods.
- `references/cloudkit.md` - CloudKit-specific constraints including uniqueness, optionality, and eventual consistency.
- `references/indexing.md` - database indexing for iOS 18+, including single and compound property indexes.
- `references/class-inheritance.md` - model subclassing for iOS 26+, including @available requirements, schema setup, and predicate filtering.