Linking Data Between Two Core Data Stores

At a glance

Project structure

Source bundle/
├── CoreDataFetchedProperty/
│   ├── AppDelegate.swift
│   ├── FeedbackViewController.swift
│   ├── MainViewController.swift
│   ├── SceneDelegate.swift
│   ├── SectionTitleView.swift
│   ├── Book+FeedbackList.swift
│   ├── Base.lproj/
│   │   └── LaunchScreen.storyboard
│   ├── CoreDataFetchedProperty.entitlements
│   └── Info.plist
├── Configuration/
│   └── SampleCode.xcconfig
└── CoreDataFetchedProperty.xcodeproj/
    ├── .xcodesamplecode.plist
    └── project.pbxproj

Structure observations

• Architecturally prominent files are ranked from entry points and role-named declarations; resource-only paths are omitted.
• Primary languages: Swift.
• The verified tree contains 8 project/configuration file(s) and 5 source declaration(s).

Overall architecture

flowchart LR
    N1["AppDelegate"]
    N2["FeedbackViewController"]
    N3["CoreData APIs"]
    N1 --> N2
    N2 --> N3

Reference code

CoreDataFetchedProperty/AppDelegate.swift:11 — architecture anchor

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
    // ...
    lazy var persistentContainer: NSPersistentContainer = {

        let container = NSPersistentContainer(name: "CoreDataFetchedProperty")
        let defaultDirectoryURL = NSPersistentContainer.defaultDirectoryURL()

        let bookStoreURL = defaultDirectoryURL.appendingPathComponent("Books.sqlite")
        let bookStoreDescription = NSPersistentStoreDescription(url: bookStoreURL)
        bookStoreDescription.configuration = "Book"

        let feedbackStoreURL = defaultDirectoryURL.appendingPathComponent("Feedback.sqlite")
        let feedbackStoreDescription = NSPersistentStoreDescription(url: feedbackStoreURL)
        feedbackStoreDescription.configuration = "Feedback"

        container.persistentStoreDescriptions = [bookStoreDescription, feedbackStoreDescription]
        container.loadPersistentStores(completionHandler: { (_, error) in
            guard let error = error as NSError? else { return }
            fatalError("###\(#function): Failed to load persistent stores:\(error)")
        })

        container.viewContext.automaticallyMergesChangesFromParent = true
        generateSampleDataIfNeeded(context: container.newBackgroundContext())

        return container
    }()
    // ...
}

Interpretation

The arrows summarize the source-visible entry, role-named types or folders, and framework direction; when nodes come from structural folders, the sequence is a high-level interpretation rather than proof that every adjacent node calls the next. Ownership is claimed only where the next section cites a stored property or assignment. The diagram is intentionally limited to the dominant path into Core Data.

Ownership and state

classDiagram
    AppDelegate o-- NSPersistentContainer : persistentContainer
    FeedbackViewController o-- UISegmentedControl : ratingSegmentedControl
    FeedbackViewController o-- UITextView : commentTextView
    FeedbackViewController o-- Book : book

Ownership evidence

CoreDataFetchedProperty/AppDelegate.swift:14 — stored dependency or nearest verified ownership anchor

    lazy var persistentContainer: NSPersistentContainer = {
        // ...
        let container = NSPersistentContainer(name: "CoreDataFetchedProperty")
        // ...
    }()

Composition arrows indicate a source-visible construction expression or locally owned value state; aggregation means the owner stores or receives a dependency without proving exclusive lifetime ownership.

Concurrency, scheduling, and thread safety

Evidence limit: actor isolation, async/await, or Task creation does not by itself prove background-thread execution; Sendable conformance alone does not prove thread-safe mutation.

No source-visible execution, scheduling, or synchronization boundary was found in the indexed source.

@MainActor/MainActor.run, DispatchQueue.main, and RunLoop.main are reported as distinct isolation, queue, and event-loop mechanisms. A plain Task is kept separate from Task.detached; neither is labeled as a background thread.

State propagation, frameworks, and dependencies

Evidence limit: an import proves a source-level compilation dependency at the cited line; it does not prove runtime use, architectural adoption, or whether a Swift package is a direct application dependency.

receive(on:) describes downstream delivery scheduling, while subscribe(on:) describes upstream subscription/request/cancel scheduling. An import Combine alone establishes neither behavior nor a Store, reducer, Redux, or other application architecture.

Class and protocol design

CoreDataFetchedProperty/AppDelegate.swift:12 — representative type boundary

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
    // ...
        let container = NSPersistentContainer(name: "CoreDataFetchedProperty")
    // ...
}

No local protocol conformance is claimed as protocol-oriented design; external framework conformances are listed only as dependencies.

Access control

Reference code

CoreDataFetchedProperty/MainViewController.swift:13 — representative boundary

    private lazy var persistentContainer: NSPersistentContainer = {
        let appDelegate = UIApplication.shared.delegate as? AppDelegate
        return appDelegate!.persistentContainer
    }()

Swift declarations without a modifier are internal; explicit private, fileprivate, private(set), public, or open entries above are interpreted by language semantics. Objective-C/C samples instead rely on header and implementation boundaries, which are not equivalent to Swift lexical privacy.

Logic ownership and placement

Design patterns

Naming conventions

• Types: Controller: FeedbackViewController, MainViewController; Delegate: AppDelegate, SceneDelegate; View: SectionTitleView.
• Protocols: no local protocol declaration in the scanned source.
• Methods: generateSampleDataIfNeeded, application, viewDidLoad, done, cancel, numberOfSections, tableView, controllerDidChangeContent.
• Files: CoreDataFetchedProperty/AppDelegate.swift, CoreDataFetchedProperty/FeedbackViewController.swift, CoreDataFetchedProperty/MainViewController.swift, CoreDataFetchedProperty/SceneDelegate.swift, CoreDataFetchedProperty/SectionTitleView.swift.

Architecture takeaways

• AppDelegate is the main source-visible entry or composition anchor for this sample.
• Framework work reaches UIKit, CoreData through a deliberately small high-level chain; the detailed API graph remains inside the cited implementation files.
• Stored-property evidence identifies lifecycle collaboration; it does not by itself prove exclusive object ownership.
• Access-control conclusions separate verified language visibility from the likely design rationale.
• The source does not justify labeling the design protocol-oriented.

Source map

• Official Apple documentation