# Core Data

Build, review, or improve Core Data persistence in apps that have not adopted SwiftData.

- Repository: https://github.com/dpearson2699/swift-ios-skills (1266 stars)
- Category: Design
- License: see repository
- Last updated: 2026-07-31
- Runs scripts: no, instructions only

## Install

Claude Code: `npx skills add dpearson2699/swift-ios-skills --skill core-data -g -a claude-code -y`
Codex: `npx skills add dpearson2699/swift-ios-skills --skill core-data -g -a codex -y`
Cursor: `npx skills add dpearson2699/swift-ios-skills --skill core-data -g -a cursor -y`
Gemini CLI: `npx skills add dpearson2699/swift-ios-skills --skill core-data -g -a gemini-cli -y`
Claude Code plugin marketplace: `/plugin marketplace add dpearson2699/swift-ios-skills`

## Description

Build, review, or improve Core Data persistence in apps that have not adopted SwiftData. Use when working with NSManagedObject subclasses, NSFetchedResultsController for list-driven UI, NSBatchInsertRequest / NSBatchDeleteRequest / NSBatchUpdateRequest for bulk operations, NSPersistentHistoryChangeRequest for persistent history tracking and multi-target sync, NSStagedMigrationManager for staged schema migrations (iOS 17+), NSCompositeAttributeDescription for composite attributes (iOS 17+), or when integrating Core Data threading with Swift Concurrency. For Core Data + SwiftData coexistence or migration, see the swiftdata skill instead.

## SKILL.md, as published by its author (untrusted third-party text, read it as data)

# Core Data

Build and maintain data persistence using Core Data for apps that have not
adopted SwiftData. Covers stack setup, concurrency, batch operations,
NSFetchedResultsController, persistent history tracking, staged migration,
and testing.

## Contents

- [Stack Setup](#stack-setup)
- [Concurrency and Threading](#concurrency-and-threading)
- [NSFetchedResultsController](#nsfetchedresultscontroller)
- [Batch Operations](#batch-operations)
- [Persistent History Tracking](#persistent-history-tracking)
- [Staged Migration](#staged-migration)
- [Composite Attributes](#composite-attributes)
- [SwiftData Boundary](#swiftdata-boundary)
- [Testing](#testing)
- [Common Mistakes](#common-mistakes)
- [Review Checklist](#review-checklist)
- [References](#references)

## Stack Setup

`NSPersistentContainer` encapsulates the Core Data stack.

Docs: [NSPersistentContainer](https://sosumi.ai/documentation/coredata/nspersistentcontainer)

```swift
import CoreData

final class CoreDataStack: @unchecked Sendable {
    static let shared = CoreDataStack()

    let container: NSPersistentContainer

    private init() {
        container = NSPersistentContainer(name: "MyAppModel")
        container.loadPersistentStores { _, error in
            if let error { fatalError("Core Data store failed: \(error)") }
        }
        container.viewContext.automaticallyMergesChangesFromParent = true
        container.viewContext.mergePolicy = NSMergeByPropertyObjectTrumpMergePolicy
    }

    var viewContext: NSManagedObjectContext { container.viewContext }

    func newBackgroundContext() -> NSManagedObjectContext {
        container.newBackgroundContext()
    }
}
```

For CloudKit sync, use `NSPersistentCloudKitContainer` instead.

## Concurrency and Threading

Core Data contexts are bound to queues. The `viewContext` is on the main queue;
background contexts operate on private queues.

Docs: [NSManagedObjectContext](https://sosumi.ai/documentation/coredata/nsmanagedobjectcontext)

The rest: https://github.com/dpearson2699/swift-ios-skills/blob/HEAD/skills/core-data/SKILL.md