custom validator not recognized in flask_wtf

Question

I have this Registrationform

class RegistrationForm(FlaskForm):
    username = StringField("username", validators=[InputRequired(), Length(min=4, max=7, message="must be between 4 and 7 Chars long")])
    email = StringField("Email", validators=[DataRequired(), Email()])
    password = PasswordField('Password', validators=[DataRequired()])
    password_repeat = PasswordField('repeat Password', validators=[DataRequired(), EqualTo('password')])
    submit = SubmitField('sign Up')

    def validate_username(self, username):
        user = User.query.filter_by(username=username.data).first()
        if user is not None:
            raise ValidationError('username allready taken.')

    def validate_email(self, email):
        user = User.query.filter_by(email=email.data).first()
        if user is not None:
            raise ValidationError('email already taken.')

    def validate_name(form, username):
        if 't' in username.data:
            raise ValidationError('no t pls')

I want to build a custom Validator to check for example if the entered username contains the letter "t" if so display an ValidationError

 def validate_name(form, username):
        if 't' in username.data:
            raise ValidationError('no t pls')

if I understood the docs correctly on Custom validators

the syntax should be correct, but I get no Error message when inserting and submitting the data
I use if form.validate_on_submit(): in routes

You don't have a form field name so the validator validate_name will never be called - or is that just a typo? — pjcunningham

Jürgen Gmach Jürgen Gmach · Accepted Answer · 2020-09-04T07:03:43

def validate_name(form, username):
    if 't' in username.data:
        raise ValidationError('no t pls')

Instead of form, you have to pass in self.

def validate_name(self, username):
    if 't' in username.data:
        raise ValidationError('no t pls')

custom validator not recognized in flask_wtf

1 Answers