Flask - wtforms: Validation always false

Question

First, I'm new to python and Flask, so I'm sorry if my question is dumb. I search it but never found an answer (which should be an "easy" one I guess).

I wanted to add a contact page in my website, I found this tutorial so I followed it. Everything worked fine until the forms validation. I only use Required and form.validate() always returned false. If I don't touch my code, and I remove every Required in the form class, it works fine, form.validate() returns true.

I don't really understand why, I read a lot that validate_on_submit() should be used, but I'm getting an error if I use it: *'ClassName' object has no attribute 'validate_on_submit'*

Here's the relevant parts of the code:

Index.py

@app.route('/contact', methods=['GET','POST'])
def contact():
form = ContactForm()

if request.method == 'POST':
    if form.validate() == False:
        flash('All Fields are required.')
        return render_template('contact.html', form=form)
    else:
        return 'Form posted'
elif request.method == 'GET':
    return render_template('contact.html', form=form)

forms.py

from wtforms import Form, TextField, TextAreaField, SubmitField, validators,ValidationError 

class ContactForm(Form):
  name = TextField("Name", [validators.Required()])
  email = TextField("Email")
  subject = TextField("Subject")
  message = TextAreaField("Message")
  submit = SubmitField("Send")

contact.html

<div id="contact">
    {% for message in get_flashed_messages() %}
        <div class="flash">{{ message }}</div>
    {% endfor %}
  <form action="{{ url_for('contact') }}" method=post>

    {{ form.name.label }}
    {{ form.name }}

    {{ form.email.label }}
    {{ form.email }}

    {{ form.subject.label }}
    {{ form.subject }}

    {{ form.message.label }}
    {{ form.message }}

    {{ form.submit }}
  </form>
 </div>

I never got the "Form posted" string even when I write something in the Name field.

Thanks in advance,

Answer 1

I always fail the form.validate_on_submit() when I am testing the login form following the demo code in Miguel Grinberg's book "Flask Web Development". So I think I should find a way to debug.

The debug approach I am taking is adding the code below to the app/auth/views.py:

flash(form.errors)

Then it shows me the culprit when I run to the login page:

errors={'csrf_token': ['CSRF token missing']}

So I recommend to use form.errors message to debug.