The 1 to 1 relation models: @Model class Country { var name: String var population: Population? init(name: String, population: Population? = nil) { self.name = name self.population = population } } @Model class Population { var country: Country? var count: Int init(country: Country? = nil, count: Int) { self.country = country self.count = count } } I don't know why not update the UI when click population label. But if I expand the CountryDetail it will works. struct DemoView: View { @Query var countries: [Country] @Environment(\.modelContext) private var context var body: some View { NavigationStack { List { ForEach(countries) { country in VStack(alignment: .leading) { Text(country.name) if let population = country.population { // bug: not update CountryDetail(population: population) // like above but expanded, it is ok Text("population: \(population.count)") .onTapGesture { Task.detached { try await DemoData(modelContainer: DemoData.sharedContainer).changePopulation() } } } } } }.safeAreaInset(edge: .bottom) { Button("Add") { let country = Country(name: "US") context.insert(country) let population = Population(country: country, count: 0) country.population = population } } } } } struct CountryDetail: View { @Bindable var population: Population var body: some View { Text("population: \(population.count)") .onTapGesture { Task.detached { try await DemoData(modelContainer: DemoData.sharedContainer).changePopulation() } } } } @ModelActor actor DemoData { static let sharedContainer = try! ModelContainer(for: Country.self, configurations: .init(isStoredInMemoryOnly: true)) func changePopulation() throws { let descriptor = FetchDescriptor<Population>() let all = try modelContext.fetch(descriptor).first if let population = try modelContext.fetch(descriptor).first { population.count += 1 try modelContext.save() print("population count", population.count) } else { fatalError("not found population") } } }