Flask WTForm not validating, no form errors reported

Question

I'm trying to setup a flask webapp with some basic login/register system controlled by flask-WTF forms.

Here is my code:

html

<!-- Register form -->
<div class="form">
    <div class="form-area">
        <h2>Register</h2>
        <form action="{{ url_for('register') }}">
            {{ form.csrf_token() }}
            {{ form.hidden_tag() }}
            {{ form.name(placeholder='name') }}
            {{ form.surname(placeholder='surname') }}
            {{ form.email(placeholder='email') }}
            {{ form.password(placeholder='password') }}
            {{ form.confirm_password(placeholder='confirm password') }}
            <input type="submit" value="Register">
        </form>
        <p>Already registered?<a href="{{ url_for('login') }}"> Log in here</a></p>
    </div>
    <div class="error-area">
        {% for error in form.confirm_password.errors %}
        <p>{{ error }}</p>
        {% endfor %}
    </div>
</div>

class

from flask_wtf import FlaskForm
from wtforms import StringField, PasswordField
from wtforms.validators import InputRequired, Length, EqualTo

class RegisterForm(FlaskForm):
    name = StringField('name', validators=[InputRequired()])
    surname = StringField('surname', validators=[InputRequired()])
    email = StringField('email', validators=[InputRequired()])
    password = PasswordField('password', validators=[InputRequired(), Length(min=6)])
    confirm_password = PasswordField('confirm passord', validators=[InputRequired(), Length(min=6), EqualTo(password)])

flask

@app.route('/register')
def register():

    #declare a register form
    form = RegisterForm()

    #validate form
    if form.validate_on_submit():
        print('validate')
        return '<h1>Success</h1>'
    else:
        print('not validated')
        print(form.errors)

    return render_template('register.html', form=form)

The problem with my code is that validation seems not to be working. Even if I fill the form with the "valid" input, form.validate_on_submit() always fail. What I can't understand is that even when I try to print array errors, no error shows.

What am I missing?

CDJB · Accepted Answer · 2020-02-06 18:33:47Z

There are a few issues here. Firstly, in your html, you haven't set a method attribute for the form. This means that it defaults to GET, which is why the form isn't validating. This can be changed like so:

<form action="{{ url_for('register') }}" method='POST'>

Incidentally, as the view that loads the form is the same as the target, you can leave out the action attribute, giving us:

<form method='POST'>

Secondly, in your class, you have a couple of issues with the confirm_password field. Firstly, you have a typo in PasswordField('confirm passord'. Secondly, the EqualTo() validator expects a string, not a field. We need to change this line in full to:

confirm_password = PasswordField('confirm password', validators=[InputRequired(), Length(min=6), EqualTo('password')])

Finally, in your flask, we need to accept POST requests to the view. This can be done by altering @app.route():

@app.route('/register', methods=['POST', 'GET'])

Having made these changes, the form should work as expected.

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