.onAppear {
   let predicate = #Predicate<Book> { book in
      book.author == nil
   }
   let sort = SortDescriptor<Book>(\.title, order: .forward)
   let descriptor = FetchDescriptor<Book>(predicate: predicate, sortBy: [sort])

   if let count = try? dbContext.fetchCount(descriptor) {
      print(count)
   }
}