Using @fetchRequest(entity: ) for SwiftUI macOS app crashes

Question

I'm trying to run a basic test SwiftUI app for macOS using Core Data, and I'm hitting a problem. When I use this in my view:

@FetchRequest(entity: Note.entity(), sortDescriptors: []) let notes: FetchedResults<Note>

The app crashes with the following errors:

NoteTaker [error] error: No NSEntityDescriptions in any model claim the NSManagedObject subclass 'NoteTaker.Note' so +entity is confused.  Have you loaded your NSManagedObjectModel yet ?
CoreData: error: No NSEntityDescriptions in any model claim the NSManagedObject subclass 'NoteTaker.Note' so +entity is confused.  Have you loaded your NSManagedObjectModel yet ?

NoteTaker [error] error: +[NoteTaker.Note entity] Failed to find a unique match for an NSEntityDescription to a managed object subclass
CoreData: error: +[NoteTaker.Note entity] Failed to find a unique match for an NSEntityDescription to a managed object subclass

NoteTaker executeFetchRequest:error: A fetch request must have an entity.

Now, if I used the alternate form of FetchRequest, it then works fine though the code is much uglier:

// outside of the view
func getAllNotes() -> NSFetchRequest<Note> {
  let request: NSFetchRequest<Note> = Note.fetchRequest()
  request.sortDescriptors = []
  return request
}

// in the view
@FetchRequest(fetchRequest: getAllNotes()) var notes: FetchedResults<Note>

Also, if I turn this into an iOS app instead, then the entity version of the @FetchRequest works fine.

Any ideas?

Answer 1

I was getting this error in several places in my code for fetching and dynamic fetching requests as well as when creating core data objects this is what worked for me:

During fetch requests I used this:

@FetchRequest(entity: NSEntityDescription.entity(forEntityName: "Your Entity Name", in: managedObjectContext), sortDescriptors: [NSSortDescriptor(key: "Your Key", ascending: true)])

In dynamic fetch requests I used this:

var entity: Entity
var fetchRequest: FetchRequest<Your Entity>
init(_ entity: Entity) {
self.entity = entity
self.fetchRequest = FetchRequest(entity: NSEntityDescription.entity(forEntityName: "Your Entity", in: managedObjectContext), sortDescriptors: [NSSortDescriptor(key: "Your Key", ascending: true)], predicate: NSPredicate(format: "entity.uniqueIdentifier == %@", entity.uniqueIdentifier!))
}

var youEntities: FetchedResults<Your Entity> {
fetchRequest.wrappedValue
}

When creating core data objects:

let entityDescription = NSEntityDescription.entity(forEntityName: "Your Entity", in: managedObjectContext)

let object = Your Entity(entity: entityDescription!, insertInto: managedObjectContext)

Answer 2

Use the Storyboard template and then set up the view using SwiftUI in the view controller.

override func viewWillAppear() {
        super.viewWillAppear()

        let context = (NSApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
        let contentView = ContentView().environment(\.managedObjectContext, context)

        view = NSHostingView(rootView: contentView)
    }

Answer 3

Adding this line: .environment(.managedObjectContext, context)

in the SceneDelegate.swift

at

// Create the SwiftUI view and set the context as the value for the managedObjectContext environment keyPath.
// Add `@Environment(\.managedObjectContext)` in the views that will need the context.
let contentView = ContentView().environment(\.managedObjectContext, context)