Fetching data in Preview: "A fetch request must have an entity UncaughtExceptionError" - core-data

Question

I have a ListView file which can build the preview code fine without the Core Data piece in it. However, when I build that ListView in the ContentView, I got an error that is not shown in the text editor like usual but in the diagnostics window. The error is "A fetch request must have an entity UncaughtExceptionError: [AppName] crashed due to an uncaught exception".
When I run the app in the simulator, the ContentView seems to build fine. (the functions attached to Text("+") don't work either, something about "map table argument is NULL", but one error at a time.)
EDIT: The entities in Core Data are set up as “Class Definition”.
Many many thanks in advance.
struct ListView: View {
#Environment(\.managedObjectContext) var viewContext
#FetchRequest(sortDescriptors: []) var targets: FetchedResults<TargetEntity>
#FetchRequest(sortDescriptors: []) var positives: FetchedResults<PositiveEntity>
var body: some View {
VStack {
HStack {
VStack {
Text("+")
.onAppear{add()}
.onTapGesture (count: 2){
do {
print("error")
increment(targets.first!)
try viewContext.save()
} catch {
print("error")
}
}
.onLongPressGesture {
addPositive()
}
List{
ForEach(positives) { item in
Text(item.title ?? "Unknown Title")
}
.onDelete(perform: deleteItems)
}
}
}
}
}
func add() {
let countnum = TargetEntity(context: viewContext)
countnum.countnum = 0
save()
}
func addPositive(){
let newPositive = PositiveEntity(context: viewContext)
newPositive.title = "Action"
save()
}
private func deleteItems(offsets: IndexSet) {
withAnimation {
offsets.map { positives[$0] }.forEach(viewContext.delete)
do {
try viewContext.save()
} catch {
let nsError = error as NSError
fatalError("Unresolved error \(nsError), \(nsError.userInfo)")
}
}
}
func save() {
do { try viewContext.save() } catch { print(error) }
}
}
struct ListView_Previews: PreviewProvider {
static var previews: some View {
NavigationView{
ListView()//.environment(\.managedObjectContext, PersistenceController.preview.container.viewContext)
}
}
}

Answer 1

Just faced same issue after updating core data model with new entity, in a project created with core data.
Error happens only to "canvas" preview, with simulator or real devices everything is ok.
Issue resolved for me by adding mock of created model to PersistenceController under the preview var