Step 5: The View Functions¶
Now that the database connections are working we can start writing the view functions. We will need four of them:
This view shows all the entries stored in the database. It listens on the root of the application and will select title and text from the database. The one with the highest id (the newest entry) will be on top. The rows returned from the cursor are tuples with the columns ordered like specified in the select statement. This is good enough for small applications like here, but you might want to convert them into a dict. If you are interested in how to do that, check out the Easy Querying example.
The view function will pass the entries as dicts to the show_entries.html template and return the rendered one:
@app.route('/') def show_entries(): cur = g.db.execute('select title, text from entries order by id desc') entries = [dict(title=row, text=row) for row in cur.fetchall()] return render_template('show_entries.html', entries=entries)
Add New Entry¶
This view lets the user add new entries if they are logged in. This only
responds to POST requests, the actual form is shown on the
show_entries page. If everything worked out well we will
flash() an information message to the next request and
redirect back to the show_entries page:
@app.route('/add', methods=['POST']) def add_entry(): if not session.get('logged_in'): abort(401) g.db.execute('insert into entries (title, text) values (?, ?)', [request.form['title'], request.form['text']]) g.db.commit() flash('New entry was successfully posted') return redirect(url_for('show_entries'))
Note that we check that the user is logged in here (the logged_in key is present in the session and True).
Be sure to use question marks when building SQL statements, as done in the example above. Otherwise, your app will be vulnerable to SQL injection when you use string formatting to build SQL statements. See Using SQLite 3 with Flask for more.
Login and Logout¶
These functions are used to sign the user in and out. Login checks the username and password against the ones from the configuration and sets the logged_in key in the session. If the user logged in successfully, that key is set to True, and the user is redirected back to the show_entries page. In addition, a message is flashed that informs the user that he or she was logged in successfully. If an error occurred, the template is notified about that, and the user is asked again:
@app.route('/login', methods=['GET', 'POST']) def login(): error = None if request.method == 'POST': if request.form['username'] != app.config['USERNAME']: error = 'Invalid username' elif request.form['password'] != app.config['PASSWORD']: error = 'Invalid password' else: session['logged_in'] = True flash('You were logged in') return redirect(url_for('show_entries')) return render_template('login.html', error=error)
The logout function, on the other hand, removes that key from the session
again. We use a neat trick here: if you use the
of the dict and pass a second parameter to it (the default), the method
will delete the key from the dictionary if present or do nothing when that
key is not in there. This is helpful because now we don’t have to check
if the user was logged in.
@app.route('/logout') def logout(): session.pop('logged_in', None) flash('You were logged out') return redirect(url_for('show_entries'))
Continue with Step 6: The Templates.