func storeBook() {
   let title = titleInput.trimmingCharacters(in: .whitespaces)
   if let year = Int(yearInput), !title.isEmpty {
      if let oldBook = appData.selectedBook {
         oldBook.title = title
         oldBook.year = year
         oldBook.author = appData.selectedAuthor
         try? dbContext.save()
      } else {
         let cover = UIImage(named: "nocover")?.pngData()
         let newBook = Book(title: title, author: appData.selectedAuthor, cover: cover, year: year)
         dbContext.insert(newBook)
         try? dbContext.save()
      }
      appData.selectedAuthor = nil
      appData.selectedBook = nil
      appData.viewPath.removeLast()
   }
}