Update Book Formular

// Display book update form on GET.
exports.book_update_get = asyncHandler(async (req, res, next) => {
  // Get book, authors and genres for form.
  const [book, allAuthors, allGenres] = await Promise.all([
    Book.findById(req.params.id).populate("author").exec(),
    Author.find().sort({ family_name: 1 }).exec(),
    Genre.find().sort({ name: 1 }).exec(),
  ]);

  if (book === null) {
    // No results.
    const err = new Error("Book not found");
    err.status = 404;
    return next(err);
  }

  // Mark our selected genres as checked.
  allGenres.forEach((genre) => {
    if (book.genre.includes(genre._id)) genre.checked = "true";
  });

  res.render("book_form", {
    title: "Update Book",
    authors: allAuthors,
    genres: allGenres,
    book: book,
  });
});

// Handle book update on POST.
exports.book_update_post = [
  // Convert the genre to an array.
  (req, res, next) => {
    if (!Array.isArray(req.body.genre)) {
      req.body.genre =
        typeof req.body.genre === "undefined" ? [] : [req.body.genre];
    }
    next();
  },

  // Validate and sanitize fields.
  body("title", "Title must not be empty.")
    .trim()
    .isLength({ min: 1 })
    .escape(),
  body("author", "Author must not be empty.")
    .trim()
    .isLength({ min: 1 })
    .escape(),
  body("summary", "Summary must not be empty.")
    .trim()
    .isLength({ min: 1 })
    .escape(),
  body("isbn", "ISBN must not be empty").trim().isLength({ min: 1 }).escape(),
  body("genre.*").escape(),

  // Process request after validation and sanitization.
  asyncHandler(async (req, res, next) => {
    // Extract the validation errors from a request.
    const errors = validationResult(req);

    // Create a Book object with escaped/trimmed data and old id.
    const book = new Book({
      title: req.body.title,
      author: req.body.author,
      summary: req.body.summary,
      isbn: req.body.isbn,
      genre: typeof req.body.genre === "undefined" ? [] : req.body.genre,
      _id: req.params.id, // This is required, or a new ID will be assigned!
    });

    if (!errors.isEmpty()) {
      // There are errors. Render form again with sanitized values/error messages.

      // Get all authors and genres for form
      const [allAuthors, allGenres] = await Promise.all([
        Author.find().sort({ family_name: 1 }).exec(),
        Genre.find().sort({ name: 1 }).exec(),
      ]);

      // Mark our selected genres as checked.
      for (const genre of allGenres) {
        if (book.genre.indexOf(genre._id) > -1) {
          genre.checked = "true";
        }
      }
      res.render("book_form", {
        title: "Update Book",
        authors: allAuthors,
        genres: allGenres,
        book: book,
        errors: errors.array(),
      });
      return;
    } else {
      // Data from form is valid. Update the record.
      const updatedBook = await Book.findByIdAndUpdate(req.params.id, book, {});
      // Redirect to book detail page.
      res.redirect(updatedBook.url);
    }
  }),
];

  hr
  p
    a(href=book.url+'/delete') Delete Book
  p
    a(href=book.url+'/update') Update Book