viewContext.execute(deleteRequest) doesn’t call redrawing SwiftUI List - core-data

Question

I don't understand when I try to remove all items by calling viewContext.execute(deleteRequest) SwiftUI doesn't redraw UI.
I see items from sqlite are gone.
struct CloudKitTestView: View {
#Environment(\.managedObjectContext) private var viewContext
#FetchRequest(
sortDescriptors: [NSSortDescriptor(keyPath: \Item.timestamp, ascending: true)],
animation: .default)
private var items: FetchedResults<Item>
var body: some View {
VStack {
Button("Remove all") {
let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "Item")
let deleteRequest = NSBatchDeleteRequest(fetchRequest: fetchRequest)
do {
try viewContext.execute(deleteRequest)
} catch {
// Replace this implementation with code to handle the error appropriately.
// fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
let nsError = error as NSError
fatalError("Unresolved error \(nsError), \(nsError.userInfo)")
}
}
List {
ForEach(items) { item in
Text("Item at \(item.timestamp!, formatter: itemFormatter)")
}
.onDelete(perform: deleteItems)
}
.toolbar {
#if os(iOS)
EditButton()
#endif
Button(action: addItem) {
Label("Add Item", systemImage: "plus")
}
}
}
}
private func addItem() {
withAnimation {
let newItem = Item(context: viewContext)
newItem.timestamp = Date()
do {
try viewContext.save()
} catch {
// Replace this implementation with code to handle the error appropriately.
// fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
let nsError = error as NSError
fatalError("Unresolved error \(nsError), \(nsError.userInfo)")
}
}
}
private func deleteItems(offsets: IndexSet) {
withAnimation {
offsets.map { items[$0] }.forEach(viewContext.delete)
do {
try viewContext.save()
} catch {
// Replace this implementation with code to handle the error appropriately.
// fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
let nsError = error as NSError
fatalError("Unresolved error \(nsError), \(nsError.userInfo)")
}
}
}
}

Answer 1

Core Data batch updates do not update the in-memory objects. You have to manually refresh afterwards.
Batch operations bypass the normal Core Data operations and operate directly on the underlying SQLite database (or whatever is backing your persistent store). They do this for benefits of speed but it means they also don't trigger all the stuff you get using normal fetch requests.
You need to do something like shown in Apple's Core Data Batch Programming Guide: Implementing Batch Updates - Updating Your Application After Execution
Original answer
do {
let fetch: NSFetchRequest<NSFetchRequestResult> = Item.fetchRequest()
let request = NSBatchDeleteRequest(fetchRequest: fetch)
request.resultType = .resultTypeObjectIDs
let result = try viewContext.execute(request) as? NSBatchDeleteResult
let objIDArray = result?.result as? [NSManagedObjectID]
let changes = [NSDeletedObjectsKey: objIDArray]
NSManagedObjectContext.mergeChanges(fromRemoteContextSave: changes, into: [viewContext])
} catch {
let nsError = error as NSError
fatalError("Unresolved error \(nsError), \(nsError.userInfo)")
}