Getting a username from a database and displaying it in HTML

Question

I'm using Flask on Python and I'm displaying the username at the top of the site (and it's working) as follows:

@app.route("/")
@login_required
def index():
    """Queries the user's First Name to display in the title"""
    names = db.execute("""
        SELECT first_name
        FROM users
        WHERE id=:user_id
        """,
        user_id = session["user_id"]
    )
    return render_template("index.html", names = names)

<header class="mainHeader">
  {% for name in names %}
    <h1>{{ name["first_name"] }}' Bookshelf</h1>
  {% else %}
    <h1>Your Bookshelf</h1>
  {% endfor %}
</header>

I don't know if it is necessary, but here is my database configuration:

Although it is working, I believe that it is not ideal to use for loop to display just one name. Does anyone have any suggestions?

Editing to include login routine:

@app.route("/login", methods=["GET", "POST"])
def login():
    """Log user in"""
    # Forget any user_id
    session.clear()

    # User reached route via POST (as by submitting a form via POST)
    if request.method == "POST":

        # Ensure email and password was submitted
        result_checks = is_provided("email") or is_provided("password")
        if result_checks is not None:
            return result_checks

        # Query database for email
        rows = db.execute("SELECT * FROM users WHERE email = ?", request.form.get("email"))

        # Ensure email exists and password is correct
        if len(rows) != 1 or not check_password_hash(rows[0]["hash"], request.form.get("password")):
            return "E-mail ou Senha inválidos"

        # Remember which user has logged in
        session["user_id"] = rows[0]["id"]
        session["email"] = request.form.get("email")

        # Redirect user to home page
        return redirect("/")

    # User reached route via GET (as by clicking a link or via redirect)
    else:
        return render_template("login.html")

Mast · Accepted Answer · 2021-05-29 23:15:08Z

according to the query, it seems that the row count is either 0 or 1. so the loop would either have no iterations (the else part) or have exactly one iteration.

in terms of performance, I think that any improvement here is not dramatic.

however, in terms of choosing the right coding tools for the job, it seems that a loop is not the right tool.

maybe the following would be better:

@app.route("/")
@login_required
def index():
    """Queries the user's First Name to display in the title"""
    names = db.execute("""
        SELECT first_name
        FROM users
        WHERE id=:user_id
        """,
        user_id = session["user_id"]    
    )
    first_name = names[0]["first_name"] if names else None
    return render_template("index.html", first_name = first_name)

and then:

<header class="mainHeader">
  {% if first_name %}
    <h1>{{ first_name }}'s Bookshelf</h1>
  {% else %}
    <h1>Your Bookshelf</h1>
  {% endif %}
</header>

note: I didn't test the code.

It is working fine! I really appreciate! The else was there because I was trying to implement an if statement and then I forgot to remove before inserting the code here. Thanks @Ron! — ARNON
– ARNON, Commented May 28, 2021 at 23:28

Kate · Accepted Answer · 2021-05-30 19:25:23Z

To be honest, this is a case where you are expecting exactly one record (right ?), given that there must be a valid session for a logged-in user. So, if anything else happens (no record or worse, more than one record) I would trigger an exception. Either there is a problem with your database or your programming logic. If I'm not wrong, this is a not a page that allows anonymous access anyway.

I assume that you use Flask-Login. Personally I use a custom User class like this, but with Flask SQL Alchemy as the ORM:

class User(UserMixin, db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(50), unique=True, nullable=False)
    # add more ...

So when the login is made some additional fields are already populated from the DB as per the data model. You just have to display them. These are session variables, so they don't have to be reloaded every time. They just have to be refreshed if they change. Your query should not hurt a lot in terms of performance but it is still slightly wasteful.

The login routine is something like this:

@cp_bp.route('/login', methods=['GET', 'POST'])
def login():
    errors = []

    if current_user.is_authenticated:
        return redirect(url_for('index'))
    form = LoginForm()

    if form.validate_on_submit():
        user = User.query.filter_by(username=form.username.data).first()
        if user is None or not user.check_password(form.password.data):
            errors.append('Invalid username or password')
            # log failure
            # return redirect(url_for('login'))
        else:
            login_user(user)

And then in my templates I can use tags like:

{{ current_user.username }}

I'm using flask_session for login and cs50 for SQL, I don't know how I could implement this. — ARNON
– ARNON, Commented May 31, 2021 at 23:03

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