Coredata - UI doesn't update after merging in SwiftUI - ios

Question

First of all, sorry for my English :) I found a weird behavior in core data with SwiftUI. After adding a new persistent store to my container, UI doesn't erase erased objects when I generate entities conflict. Merge policy was NSMergeByPropertyObjectTrumpMergePolicy so existing object in the store might be overwritten by new object, but they still appears with 'nil' values. Let's look at my codes.
My core data model looks like:
Core data singleton:
struct PersistenceController {
static let shared = PersistenceController()
let container: NSPersistentContainer
init() {
container = NSPersistentContainer(name: "CoredataTest")
// Adding new stores makes problem!!
let defaultURL = NSPersistentContainer.defaultDirectoryURL()
let newURL = defaultURL.appendingPathComponent("MyStore.sqlite")
container.persistentStoreDescriptions += [NSPersistentStoreDescription(url: newURL)]
container.loadPersistentStores(completionHandler: { (storeDescription, error) in
if let error = error as NSError? {
fatalError("Unresolved error \(error), \(error.userInfo)")
}
})
container.viewContext.mergePolicy = NSMergeByPropertyObjectTrumpMergePolicy
container.viewContext.automaticallyMergesChangesFromParent = true
}
static func testConflict() {
let newPerson = Person(context: shared.container.viewContext)
newPerson.id = UUID()
newPerson.name = "Jack"
try! shared.container.viewContext.save()
let conflict = Person(context: shared.container.viewContext)
// Same id to test conflict
conflict.id = newPerson.id
conflict.name = "Another Jack"
try! shared.container.viewContext.save()
}
}
The new persistent store was never used. It's just for demonstrating core data's weird stuff.
UI:
struct ContentView: View {
#Environment(\.managedObjectContext) private var viewContext
#FetchRequest(
sortDescriptors: [NSSortDescriptor(keyPath: \Person.name, ascending: true)],
animation: .default)
private var people: FetchedResults<Person>
var body: some View {
NavigationView {
List {
ForEach(people) { person in
Text(person.name ?? "nil")
}
}
.toolbar {
ToolbarItem {
Button(action: PersistenceController.testConflict) {
Label("Make doppelganger", systemImage: "wand.and.stars")
}
}
}
}
}
}
When I tap the wand button to test conflict, that happens I just introduced you.
I tapped twice. There's nil objects which were "Jack" objects that doesn't exist anymore. They disappears when I close the app and launch it again that means they were erased in the store actually but UI still refers them in memory in some reasons.
It doesn't happen if I use only one persistent store. So, I guess using multiple persistent store is related but I have no ideas how to find the reason.
Of course, I can simply filter the nil objects to hide in the UI but I still want to know why this happens and there is any way to fix the fundamental problem.