Hello, Amateur developer here. I dusted off a hobby core data app coded mostly under OSX 10.7, and which supported undo "for free" (as Apple say it). It still works when I build it with recent Xcode versions, except that it no longer supports undo. To understand why, I coded the most basic objective-C, core data (not document-based) app. In short, a single table view with a single column bound to an NSArray Controller set in "entity name" mode and bound to the managed object context. The core data model has a single entity class with a single NSString attribute (called "name", and which the table view column shows). It all works well, I can add and remove entities, and change their names from the table. Changes are saved normally... except there is nothing I can undo. The undo menu item is greyed out. I checked that my App Delegate implements the windowWillReturnUndoManager method and that this selector is called regularly. So to check that the undo manager sees anything to undo, I added this method to my App Delegate: - (IBAction)reportUndo:(id)sender {     NSLog(@"undo: %d", [self.persistentContainer.viewContext.undoManager canUndo]); } I can call this method by pressing a button. But it always logs "undo: 0", even after I add or remove entities. I take that the undo manager sees nothing to undo. This seems like rather basic stuff, but I can't understand why it doesn't work give given that it used to work in my more complex app without me doing anything special.