Core Data

What is Core Data?

Core Data is Apple's object graph and persistence framework. It manages object lifecycles, relationships, and serialization to SQLite.

NSPersistentContainer

The container manages the entire Core Data stack:

import CoreData

let container = NSPersistentContainer(name: "MyApp")
container.loadPersistentStores { description, error in
    if let error = error {
        fatalError("Core Data failed to load: \(error.localizedDescription)")
    }
}
let context = container.viewContext

Stack Components

• NSManagedObjectContext: In-memory scratchpad for objects
• NSPersistentStoreCoordinator: Manages persistent stores
• NSManagedObjectModel: Defines your data model

Background Context

For heavy operations off the main thread:

let backgroundContext = container.newBackgroundContext()
backgroundContext.perform {
    let obj = NSEntityDescription.insertNewObject(forEntityName: "Article", into: backgroundContext)
    try? backgroundContext.save()
}

SwiftUI Integration

@main
struct MyApp: App {
    let container: NSPersistentContainer
    init() {
        container = NSPersistentContainer(name: "MyApp")
        container.loadPersistentStores { _, error in
            if let error = error { fatalError("Failed: \(error)") }
        }
    }
    var body: some Scene {
        WindowGroup { ContentView() }
            .environment(\.managedObjectContext, container.viewContext)
    }
}

NSManagedObject Subclasses

Generate or create typed subclasses:

@objc(Article)
public class Article: NSManagedObject {
    @NSManaged public var id: UUID
    @NSManaged public var title: String
    @NSManaged public var content: String
    @NSManaged public var publishedAt: Date
    @NSManaged public var author: Author?
}

extension Article {
    @nonobjc public class func fetchRequest() -> NSFetchRequest<Article> {
        return NSFetchRequest<Article>(entityName: "Article")
    }
}

Creating and Saving

let article = Article(context: context)
article.id = UUID()
article.title = "Hello World"
article.publishedAt = Date()
try? context.save()

Relationships

@objc(Author)
public class Author: NSManagedObject {
    @NSManaged public var name: String
    @NSManaged public var articles: NSSet?
}

// Access
if let articles = author.articles?.allObjects as? [Article] {
    for article in articles { print(article.title) }
}

// Set
author.addToArticles(article)

Basic Fetch

let request = NSFetchRequest<NSFetchRequestResult>(entityName: "Article")
let articles = try context.fetch(request) as? [Article] ?? []

Predicates

request.predicate = NSPredicate(format: "isPublished == %@", NSNumber(value: true))
request.predicate = NSPredicate(format: "title CONTAINS[cd] %@", searchText)
request.predicate = NSPredicate(format: "publishedAt > %@", lastWeek as NSDate)

let compound = NSCompoundPredicate(andPredicateWithSubpredicates: [
    NSPredicate(format: "isPublished == %@", true),
    NSPredicate(format: "title CONTAINS %@", searchText)
])
request.predicate = compound

Sorting and Limits

request.sortDescriptors = [
    NSSortDescriptor(key: "publishedAt", ascending: false),
    NSSortDescriptor(key: "title", ascending: true)
]
request.fetchLimit = 20
request.fetchOffset = 0
request.fetchBatchSize = 20

Batch Operations

Delete multiple objects efficiently:

let batchDelete = NSBatchDeleteRequest(fetchRequest: Article.fetchRequest())
try? context.execute(batchDelete)

// Batch update
let batchUpdate = NSBatchUpdateRequest(entityName: "Article")
batchUpdate.predicate = NSPredicate(format: "isPublished == %@", false)
batchUpdate.propertiesToUpdate = ["isPublished": true]
try? context.execute(batchUpdate)

Async Fetch

let fetchRequest = Article.fetchRequest()
fetchRequest.predicate = NSPredicate(format: "isPublished == %@", true)

let articles = try await context.perform {
    try self.context.fetch(fetchRequest)
}