How to validate in Flask Forms under certain conditions?

Question

I want the po_count and cpe_count fields only when the license_type is Production. The record is not going in the database which is what I want but it is not throwing messages when the user does not give values when the type is Production

class LicenseRequestForm(FlaskForm): salesperson = StringField('Salesperson Name', validators=[DataRequired()]) license_type_choices = [('Lab', 'Lab'), ('Production', 'Production')] license_type = SelectField('License Type', choices=license_type_choices, validators=[DataRequired()]) po_count = IntegerField('PO Count', validators=[Optional()]) cpe_count = IntegerField('Number of CPEs', validators=[Optional()])

ha = BooleanField('High Availability (HA) Option')


file1 = FileField('NodeID File 1', validators=[DataRequired()])
file2 = FileField('NodeID File 2', validators=[Optional()])

submit = SubmitField('Submit')

def validate(self, extra_validators=None):
    if self.license_type.data == 'Production':
        self.po_count.validators = [DataRequired()]
        self.cpe_count.validators = [DataRequired()]
    elif self.license_type.data == 'Lab':
        self.po_count.validators = [Optional()]
        self.cpe_count.validators = [Optional()]

    if self.ha.data:
        self.file1.validators = [DataRequired()]
        self.file2.validators = [DataRequired()]
    else:
        self.file2.validators = [Optional()]

    return super().validate()

I tried the validate method but still it did not show any message.

Answer 1

Maybe I'm getting something wrong, but let me get this forward

The user set license_type to PRO and is not giving values for po & cpe count and because this information is not enough, you'd like to give some kind of message like: 'Please set po, cpe count values'

If that's the case, flask offers flash, which is a message that it will be displayed if the user bad use the form, is really straight forward.

docs: https://flask.palletsprojects.com/en/2.3.x/patterns/flashing/

video explaining: https://www.youtube.com/watch?v=UIJKdCIEXUQ starting at timestamp 25:10

If this doesn't reply completely to your question, I'm pretty sure that you'll get your answer in the video attached above, also regarding data validation.

Kind regards!