In this exercise we combine database queries with Jinja templates. In the routes.py file, besides the home() route listing all the books in the database, we also added several routes for displaying web pages with filtered entries from the database. For example,

@app.route('/books/<year>')
def books(year):
   books = Book.query.filter_by(year = year)
   return render_template('display_books.html', year = year, books = books)

is a dynamic route with the year variable that can be set to some valid year in the URL. Next, we filter out the books from the asked year and display them using the display_books.html file (you can find in the templates folder). The template expects the provided year and a list of books to display.

In the URL bar of the integrated Web browser on the right, type or copy-paste the following: http://localhost:8000/books/2020. You see all the books suggested in 2020, together with all the reviews for each book. Cool, ha?

If the list of the retrieved queries is empty, we handle that in the display_books.html template by outputting that there are no books suggested in that year. Alternatively, one can use .first_or_404() as we do in the following:

reader = Reader.query.filter_by(id = user_id).first_or_404(description = "There is no user with this ID.")

If a reader with some id does not exist in the database, 404 error is returned with a custom made message.

Take some time to observe the complete code provided on the right paying attention to routes.py, and explore the templates in the template folder.