swiftdata

This skill provides comprehensive guidance for implementing data persistence in iOS applications using SwiftData, Apple's modern data framework introduced in iOS 17 and refined through iOS 26. It addresses the challenge of building robust, type-safe data models with automatic persistence, CloudKit synchronization, and efficient querying capabilities. The skill helps developers transition from Core Data to SwiftData's declarative API or build new persistence layers from scratch using Swift's modern language features including macros, structured concurrency, and property wrappers.

The skill covers the full spectrum of SwiftData capabilities, from defining models with @Model, @Attribute, @Relationship, and @Transient macros to configuring ModelContainer for local or cloud-synced storage. It provides detailed guidance on querying data using @Query property wrappers, #Predicate expressions, FetchDescriptor, and SortDescriptor. Advanced topics include schema versioning with VersionedSchema, migration planning with SchemaMigrationPlan, background processing with @ModelActor, and proper CloudKit sync configuration including required app entitlements. The skill also addresses model inheritance (iOS 26+), compound uniqueness constraints with #Unique (iOS 18+), and attribute options like external storage and spotlight integration.

This skill is designed for iOS developers building applications that require structured data persistence, whether creating new projects or migrating from Core Data. It's particularly valuable for teams implementing features like offline-first architectures, multi-device sync via CloudKit, complex data relationships, or apps requiring schema evolution over time. The skill includes a review checklist and common mistakes section to help both implement new code and audit existing SwiftData implementations for correctness, performance, and maintainability.