Core Data in 2025: Modern Persistence Patterns for SwiftUI and Concurrency

enum Persistence {
  static let container: NSPersistentContainer = {
    let c = NSPersistentContainer(name: "Model")
    c.loadPersistentStores { _, error in precondition(error == nil, "Store error: \(String(describing: error))") }
    c.viewContext.mergePolicy = NSMergeByPropertyObjectTrumpMergePolicy
    c.viewContext.automaticallyMergesChangesFromParent = true
    return c
  }()

  static var viewContext: NSManagedObjectContext { container.viewContext }
  static func bgContext() -> NSManagedObjectContext { container.newBackgroundContext() }
}

extension NSManagedObjectContext {
  func performAsync<T>(_ work: @escaping (NSManagedObjectContext) throws -> T) async throws -> T {
    try await withCheckedThrowingContinuation { cont in
      self.perform {
        do { cont.resume(returning: try work(self)) }
        catch { cont.resume(throwing: error) }
      }
    }
  }
}

struct ArticleDTO: Decodable { let id: UUID; let title: String }

func upsertArticles(_ dtos: [ArticleDTO]) async throws {
  let ctx = Persistence.bgContext()
  try await ctx.performAsync { ctx in
    for dto in dtos {
      let req: NSFetchRequest<Article> = Article.fetchRequest()
      req.predicate = NSPredicate(format: "id == %@", dto.id as CVarArg)
      let obj = try ctx.fetch(req).first ?? Article(context: ctx)
      obj.id = dto.id
      obj.title = dto.title
    }
    if ctx.hasChanges { try ctx.save() }
  }
}

@main
struct AppMain: App {
  var body: some Scene {
    WindowGroup {
      FeedView()
        .environment(\.managedObjectContext, Persistence.viewContext)
    }
  }
}

struct FeedView: View {
  @FetchRequest(sortDescriptors: [NSSortDescriptor(keyPath: \Article.title, ascending: true)])
  private var articles: FetchedResults<Article>

  var body: some View {
    List(articles) { Text($0.title ?? "") }
  }
}

final class PersistenceTests: XCTestCase {
  func testInsertFetch() throws {
    let c = NSPersistentContainer(name: "Model")
    let desc = NSPersistentStoreDescription()
    desc.type = NSInMemoryStoreType
    c.persistentStoreDescriptions = [desc]
    c.loadPersistentStores(completionHandler: {_,_ in })

    let ctx = c.viewContext
    let a = Article(context: ctx); a.id = UUID(); a.title = "Hello"
    try ctx.save()

    let req: NSFetchRequest<Article> = Article.fetchRequest()
    let results = try ctx.fetch(req)
    XCTAssertEqual(results.count, 1)
  }
}