core-data

Name: core-data
Author: dpearson2699

915stars45forks

How to install core-data?

dpearson2699/swift-ios-skills/core-data

$npx -y skills add dpearson2699/swift-ios-skills --skill core-data

Installs into the current project.

Summary

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, NSPers

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SKILL.md

1	# Core Data
2
3	Build and maintain data persistence using Core Data for apps that have not
4	adopted SwiftData. Covers stack setup, concurrency, batch operations,
5	NSFetchedResultsController, persistent history tracking, staged migration,
6	and testing.
7
8	## Contents
9
10	- [Stack Setup](#stack-setup)
11	- [Concurrency and Threading](#concurrency-and-threading)
12	- [NSFetchedResultsController](#nsfetchedresultscontroller)
13	- [Batch Operations](#batch-operations)
14	- [Persistent History Tracking](#persistent-history-tracking)
15	- [Staged Migration](#staged-migration)
16	- [Composite Attributes](#composite-attributes)
17	- [SwiftData Boundary](#swiftdata-boundary)
18	- [Testing](#testing)
19	- [Common Mistakes](#common-mistakes)
20	- [Review Checklist](#review-checklist)
21	- [References](#references)
22
23	## Stack Setup
24
25	`NSPersistentContainer` encapsulates the Core Data stack.
26
27	Docs: [NSPersistentContainer](https://sosumi.ai/documentation/coredata/nspersistentcontainer)
28
29	```swift
30	import CoreData
31
32	final class CoreDataStack: @unchecked Sendable {
33	static let shared = CoreDataStack()
34
35	let container: NSPersistentContainer
36
37	private init() {
38	container = NSPersistentContainer(name: "MyAppModel")
39	container.loadPersistentStores { _, error in
40	if let error { fatalError("Core Data store failed: \(error)") }
41	}
42	container.viewContext.automaticallyMergesChangesFromParent = true
43	container.viewContext.mergePolicy = NSMergeByPropertyObjectTrumpMergePolicy
44	}
45
46	var viewContext: NSManagedObjectContext { container.viewContext }
47
48	func newBackgroundContext() -> NSManagedObjectContext {
49	container.newBackgroundContext()
50	}
51	}
52	```
53
54	For CloudKit sync, use `NSPersistentCloudKitContainer` instead.
55
56	## Concurrency and Threading
57
58	Core Data contexts are bound to queues. The `viewContext` is on the main queue;
59	background contexts operate on private queues.
60
61	Docs: [NSManagedObjectContext](https://sosumi.ai/documentation/coredata/nsmanagedobjectcontext)
62
63	Rules:
64	- Always use `perform(_:)` or `performAndWait(_:)` when accessing a context
65	off its own queue.
66	- Never pass `NSManagedObject` instances across context or thread boundaries.
67	Pass `NSManagedObjectID` instead and re-fetch.
68	- Set `automaticallyMergesChangesFromParent = true` on the `viewContext`.
69
70	```swift
71	// Writing on a background context
72	func updateTrip(id: NSManagedObjectID, newName: String) async throws {
73	let context = CoreDataStack.shared.newBackgroundContext()
74	try await context.perform {
75	guard let trip = try context.existingObject(with: id) as? CDTrip else {
76	throw PersistenceError.notFound
77	}
78	trip.name = newName
79	try context.save()
80	}
81	}
82	```
83
84	### Swift Concurrency Integration
85
86	`NSManagedObjectContext.perform(_:)` has an `async throws` overload
87	(iOS 15+). Avoid marking `NSManagedObject` subclasses as `Sendable`.
88
89	```swift
90	func importItems(_ records: [ItemRecord]) async throws {
91	let context = CoreDataStack.shared.newBackgroundContext()
92	try await context.perform {
93	for record in records {
94	let item = CDItem(context: context)
95	item.id = record.id
96	item.title = record.title
97	}
98	try context.save()
99	}
100	// After save completes, viewContext auto-merges if configured
101	}
102	```
103
104	Do not use `@unchecked Sendable` on managed objects. If you need
105	cross-boundary communication, pass the `objectID` (which is `Sendable`)
106	and re-fetch:
107
108	```swift
109	let objectID = trip.objectID // Sendable
110	Task.detached {
111	let bgContext = CoreDataStack.shared.newBackgroundContext()
112	try await bgContext.perform {
113	let trip = try bgContext.existingObject(with: objectID) as! CDTrip
114	trip.isFavorite = true
115	try bgContext.save()
116	}
117	}
118	```
119
120	## NSFetchedResultsController
121
122	Efficiently drives `UITableView` / `UICollectionView` from a Core Data fetch
123	request, with built-in change tracking and optional caching.
124
125	Docs: [NSFetchedResultsController](https://sosumi.ai/documentation/coredata/nsfetchedresultscontroller)
126
127	```swift
128	import CoreData
129	import UIKit
130
131	class TripsViewController: UITableViewController, NSFetchedResultsControllerDelegate {
132
133	private lazy var fetchedResultsController: NSFetchedResultsController<CDTrip> = {
134	let request: NSFetchRequest<CDTrip> = C

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core-data

915stars45forks

View on GitHub

How to install core-data?

dpearson2699/swift-ios-skills/core-data

$npx -y skills add dpearson2699/swift-ios-skills --skill core-data

Installs into the current project.

Summary

Files · 1

View on GitHub

SKILL.md

1	# Core Data
2
3	Build and maintain data persistence using Core Data for apps that have not
4	adopted SwiftData. Covers stack setup, concurrency, batch operations,
5	NSFetchedResultsController, persistent history tracking, staged migration,
6	and testing.
7
8	## Contents
9
10	- [Stack Setup](#stack-setup)
11	- [Concurrency and Threading](#concurrency-and-threading)
12	- [NSFetchedResultsController](#nsfetchedresultscontroller)
13	- [Batch Operations](#batch-operations)
14	- [Persistent History Tracking](#persistent-history-tracking)
15	- [Staged Migration](#staged-migration)
16	- [Composite Attributes](#composite-attributes)
17	- [SwiftData Boundary](#swiftdata-boundary)
18	- [Testing](#testing)
19	- [Common Mistakes](#common-mistakes)
20	- [Review Checklist](#review-checklist)
21	- [References](#references)
22
23	## Stack Setup
24
25	`NSPersistentContainer` encapsulates the Core Data stack.
26
27	Docs: [NSPersistentContainer](https://sosumi.ai/documentation/coredata/nspersistentcontainer)
28
29	```swift
30	import CoreData
31
32	final class CoreDataStack: @unchecked Sendable {
33	static let shared = CoreDataStack()
34
35	let container: NSPersistentContainer
36
37	private init() {
38	container = NSPersistentContainer(name: "MyAppModel")
39	container.loadPersistentStores { _, error in
40	if let error { fatalError("Core Data store failed: \(error)") }
41	}
42	container.viewContext.automaticallyMergesChangesFromParent = true
43	container.viewContext.mergePolicy = NSMergeByPropertyObjectTrumpMergePolicy
44	}
45
46	var viewContext: NSManagedObjectContext { container.viewContext }
47
48	func newBackgroundContext() -> NSManagedObjectContext {
49	container.newBackgroundContext()
50	}
51	}
52	```
53
54	For CloudKit sync, use `NSPersistentCloudKitContainer` instead.
55
56	## Concurrency and Threading
57
58	Core Data contexts are bound to queues. The `viewContext` is on the main queue;
59	background contexts operate on private queues.
60
61	Docs: [NSManagedObjectContext](https://sosumi.ai/documentation/coredata/nsmanagedobjectcontext)
62
63	Rules:
64	- Always use `perform(_:)` or `performAndWait(_:)` when accessing a context
65	off its own queue.
66	- Never pass `NSManagedObject` instances across context or thread boundaries.
67	Pass `NSManagedObjectID` instead and re-fetch.
68	- Set `automaticallyMergesChangesFromParent = true` on the `viewContext`.
69
70	```swift
71	// Writing on a background context
72	func updateTrip(id: NSManagedObjectID, newName: String) async throws {
73	let context = CoreDataStack.shared.newBackgroundContext()
74	try await context.perform {
75	guard let trip = try context.existingObject(with: id) as? CDTrip else {
76	throw PersistenceError.notFound
77	}
78	trip.name = newName
79	try context.save()
80	}
81	}
82	```
83
84	### Swift Concurrency Integration
85
86	`NSManagedObjectContext.perform(_:)` has an `async throws` overload
87	(iOS 15+). Avoid marking `NSManagedObject` subclasses as `Sendable`.
88
89	```swift
90	func importItems(_ records: [ItemRecord]) async throws {
91	let context = CoreDataStack.shared.newBackgroundContext()
92	try await context.perform {
93	for record in records {
94	let item = CDItem(context: context)
95	item.id = record.id
96	item.title = record.title
97	}
98	try context.save()
99	}
100	// After save completes, viewContext auto-merges if configured
101	}
102	```
103
104	Do not use `@unchecked Sendable` on managed objects. If you need
105	cross-boundary communication, pass the `objectID` (which is `Sendable`)
106	and re-fetch:
107
108	```swift
109	let objectID = trip.objectID // Sendable
110	Task.detached {
111	let bgContext = CoreDataStack.shared.newBackgroundContext()
112	try await bgContext.perform {
113	let trip = try bgContext.existingObject(with: objectID) as! CDTrip
114	trip.isFavorite = true
115	try bgContext.save()
116	}
117	}
118	```
119
120	## NSFetchedResultsController
121
122	Efficiently drives `UITableView` / `UICollectionView` from a Core Data fetch
123	request, with built-in change tracking and optional caching.
124
125	Docs: [NSFetchedResultsController](https://sosumi.ai/documentation/coredata/nsfetchedresultscontroller)
126
127	```swift
128	import CoreData
129	import UIKit
130
131	class TripsViewController: UITableViewController, NSFetchedResultsControllerDelegate {
132
133	private lazy var fetchedResultsController: NSFetchedResultsController<CDTrip> = {
134	let request: NSFetchRequest<CDTrip> = C

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