[SwiftData] Bugs with `autosaveEnabled` and `undoManager` + Observation

Hello,

my goal is it to implement an Edit Sheet of a Model with Discard changes in SwiftData.

• Xcode Version 15.0 beta 6 (15A5219j)

Approaches

In the following modelContext refers to the context fetched from the environment by the View. Also code for showing the sheet (eg. toggling isPresented) is omitted.

// App
ContentView()
    .modelContainer(for: Model.self, isAutosaveEnabled: true, isUndoEnabled: true)

// In Content View
@Query var models: [Model]
//...
ForEach(models) { model in
    ModelView(model: model)
        //eg. longpresgesture that calls openEditSheet
        .sheet(..., content: {
            EditModelView(model: model)
        }
}

Disabling autosave + rollback

// In ContentView
func openEditSheet() {
    modelContext.autosaveEnabled = false
}

// In EditModelView
func discardEditSheet() {
    modelContext.rollback()
    modelContext.autosaveEnabled = true
}

func saveEditSheet() {
    try? modelContext.save() // probably not needed if autosave gets enabled anyway
    modelContext.autosaveEnabled = true
}

However this approach does not work, as SwiftData continues to save anyway and therefore there is nothing to rollback.

modelContext in Memory

// In ContentView
let context = ModelContext(modelContext.container)
context.autosaveEnabled = false
context.container.configuration.removeAll()
context.container.configuration.insert(ModelConfiguration(..., inMemory: true)
//...
EditModelView()
    .modelContext(context)
    // Also tried: .enviroment(\.modelContext, context)

// In EditModelView
func discardEditSheet() {
    modelContext.rollback() // probably not needed as the container is never saved
}

func saveEditSheet() {
    try? modelContext.save() // move to persistent storage from memory
}

• The idea was to use something like parent in CoreData. However as this is (currently) not supported.
• Also tried this by modifying the modelContext directly (instead of creating a new context) and its container directly or before creating the context.
• The child can not be a ModelContainer as you can not pass a context to it or set its mainContext (get-only).

However this approach does not work, as the container does not seem to stay in memory. Maybe related to previous.

BackingData

EditModelView(model: Model(backingData: model.persistentBackingData)

• not sure about this one, played around a little with it but not sure what it means / should mean and how I would expect it to work. I have never been great at cooking :).

UndoManager (preferred)

// In ContentView
func openEditSheet() {
    modelContext.undoManager?.beginUndoGrouping()
}

// In EditModelView
func discardEditSheet() {
    modelContext.undoManager?.endUndoGrouping()
    modelContext.undoManager?.undoNestedGroup()
    // Also tried adding: try? modelContext.save()
}

func saveEditSheet() {
    modelContext.undoManager?.endUndoGrouping()
}

This approach does works kinda weird:

• The ModelView of the updated model in ContentView's ForEach is not updated regarding the undo action.
• However when I re-open the EditTaskView of the updated model it has the expected state, even though the model to edit is passed by the ContentView (which does not have the correct state?).
• After relaunching the app or when modifying the model again (this time not undoing) the previous sate changes are recognised

Therefore this looks like it does what I want, with the ContentView having the correct state, but not displaying it. Only reason I can think of is the Model: Observable not getting triggered and therefore no View update.

Conclusion

After playing around with the above approaches and combining them in every possible way, i think that:

• disabling autosave at runtime is currently not working and this is a bug (otherwise autosaveEnabled should be get-only).
• UndoManager does not trigger a View update of a Model/Observable and this is a bug

Would be happy to hear other opinions on this. Am I missing something here? Am I ******?

Question

However as my conclusion does not fix my problem I am wondering:

• Are my approaches (theoretically) correct?
• How do I fix / workaround the UndoManager issue? If I identified it correctly, how can I manually notify the view that a Observable model has changed?