Swiftdata Pro

1---2name: swiftdata-pro3description: Writes, reviews, and improves SwiftData code using modern APIs and best practices. Use when reading, writing, or reviewing projects that use SwiftData.4license: MIT5metadata:6  author: Paul Hudson7  version: "1.0"8---9 10Write and review SwiftData code for correctness, modern API usage, and adherence to project conventions. Report only genuine problems - do not nitpick or invent issues.11 12Review process:13 141. Check for core SwiftData issues using `references/core-rules.md`.151. Check that predicates are safe and supported using `references/predicates.md`.161. If the project uses CloudKit, check for CloudKit-specific constraints using `references/cloudkit.md`.171. If the project targets iOS 18+, check for indexing opportunities using `references/indexing.md`.181. If the project targets iOS 26+, check for class inheritance patterns using `references/class-inheritance.md`.19 20If doing partial work, load only the relevant reference files.21 22 23## Core Instructions24 25- Target Swift 6.2 or later, using modern Swift concurrency.26- 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.27- Do not introduce third-party frameworks without asking first.28- Use a consistent project structure, with folder layout determined by app features.29 30 31## Output Format32 33If the user asks for a review, organize findings by file. For each issue:34 351. State the file and relevant line(s).362. Name the rule being violated.373. Show a brief before/after code fix.38 39Skip files with no issues. End with a prioritized summary of the most impactful changes to make first.40 41If 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.42 43Example output:44 45### Destination.swift46 47**Line 8: Add an explicit delete rule for relationships.**48 49```swift50// Before51var sights: [Sight]52 53// After54@Relationship(deleteRule: .cascade, inverse: \Sight.destination) var sights: [Sight]55```56 57**Line 22: Do not use `isEmpty == false` in predicates – it crashes at runtime. Use `!` instead.**58 59```swift60// Before61#Predicate<Destination> { $0.sights.isEmpty == false }62 63// After64#Predicate<Destination> { !$0.sights.isEmpty }65```66 67### DestinationListView.swift68 69**Line 5: `@Query` must only be used inside SwiftUI views.**70 71```swift72// Before73class DestinationStore {74    @Query var destinations: [Destination]75}76 77// After78class DestinationStore {79    var modelContext: ModelContext80 81    func fetchDestinations() throws -> [Destination] {82        try modelContext.fetch(FetchDescriptor<Destination>())83    }84}85```86 87### Summary88 891. **Data loss (high):** Missing delete rule on line 8 of Destination.swift means sights will be orphaned when a destination is deleted.902. **Crash (high):** `isEmpty == false` on line 22 will crash at runtime – use `!isEmpty` instead.913. **Incorrect behavior (high):** `@Query` on line 5 of DestinationListView.swift only works inside SwiftUI views.92 93End of example.94 95 96## References97 98- `references/core-rules.md` - autosaving, relationships, delete rules, property restrictions, and FetchDescriptor optimization.99- `references/predicates.md` - supported predicate operations, dangerous patterns that crash at runtime, and unsupported methods.100- `references/cloudkit.md` - CloudKit-specific constraints including uniqueness, optionality, and eventual consistency.101- `references/indexing.md` - database indexing for iOS 18+, including single and compound property indexes.102- `references/class-inheritance.md` - model subclassing for iOS 26+, including @available requirements, schema setup, and predicate filtering.