Agent skill

iOS Persistence

Standards for SwiftData, Core Data, and Local Storage.

View SKILL.md on GitHub Repository
Stars 163
Forks 31

Install this agent skill to your Project

npx add-skill https://github.com/majiayu000/claude-skill-registry/tree/main/skills/other/other/persistence

Metadata

Additional technical details for this skill

labels
ios persistence swiftdata coredata sqlite
triggers 
{
    "files": [
        "**/*.xcdatamodeld",
        "**/*Model.swift"
    ],
    "keywords": [
        "PersistentContainer",
        "FetchRequest",
        "ManagedObject",
        "Query",
        "ModelContainer",
        "Repository"
    ]
}

SKILL.md

iOS Persistence Standards

Priority: P0

Implementation Guidelines

SwiftData (iOS 17+)

  • Models: Use @Model macro for pure Swift classes.
  • Container: Use ModelContainer for schema management. Inject into the environment for SwiftUI apps.
  • Queries: Use @Query for declarative data fetching in Views.

Core Data (Standard)

  • Persistent Stack: Initialize NSPersistentContainer in a dedicated PersistenceController.
  • Context Management: Use viewContext for UI tasks and newBackgroundContext() for heavy imports to avoid blocking the main thread.
  • FetchedResultsController: Use NSFetchedResultsController for efficient list management with change tracking.

Best Practices

  • Migration: Always perform lightweight migrations for minor schema changes. Use versioned models for complex migrations.
  • Threading: Managed objects are not thread-safe. Always access them on the context's queue (e.g., perform { ... }).
  • Batching: Use NSBatchUpdateRequest or NSBatchDeleteRequest for large datasets.

Anti-Patterns

  • Main Thread Blocking: **No heavy I/O on ViewContext**: Use private background contexts.
  • Manual String Keys: **No string-based predicates**: Use KeyPaths or generated helpers.
  • Missing Merge Policies: **No merge strategy**: Explicitly set mergePolicy (e.g., mergeByPropertyObjectTrump).

References

  • SwiftData & Core Data Implementation

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