Using SwiftUI, Core Data, and one-to-many relationships, why does the list not update when adding a row on the Many side

Question

I have a SwiftUI project with Core Data. The data model is a simple one-to-many and two primary views which each have a textfield at the top and a button to add a new item to th

Answer 1

The only thing I could come up with as a way to make it work decently well was to create a new FetchRequest for the Many items using the selected One in a predicate. Adding the FetchRequest and an init to the beginning of the OneDetailView allows for the list to update.

struct OneDetailView: View {
@Environment(\.managedObjectContext) var moc

@ObservedObject var one: One

@State private var newManyAttribute = ""
@Binding var isNavTitleHidden: Bool

@FetchRequest var manys: FetchedResults

init(one: One, isNavTitleHidden: Binding) {
    self.one = one
    self._isNavTitleHidden = isNavTitleHidden
    var predicate: NSPredicate?
    predicate = NSPredicate(format: "one = %@", one)
    self._manys = FetchRequest(
        entity: Many.entity(),
        sortDescriptors: [],
        predicate: predicate
    )
}

var body: some View {
    VStack {
        HStack {
            TextField("New Many", text: self.$newManyAttribute)
            Spacer()
            Button(action: {
                let newMany = Many(context: self.moc)
                newMany.attribute = self.newManyAttribute
                self.newManyAttribute = ""
                self.one.addToMany(newMany)
                try? self.moc.save()
            }) {
                Image(systemName: "plus.circle.fill")
                    .foregroundColor(.green)
                    .frame(width: 32, height: 32, alignment: .center)
            }
        }
        .padding(.top)
        .padding(.horizontal)

        List {
            Section(header: Text("Manys")) {
                ForEach(self.manys, id: \.self) { many in
                    ManyView(many: many).environment(\.managedObjectContext, self.moc)
                }
            }
        }
    }
    .navigationBarTitle("\(self.one.wrappedName) Details")
    .onAppear {
        self.isNavTitleHidden = false
    }
}}