Flask form not displaying errors when I use custom validators

I'm creating custom validators for my Flask form inputs and as an example, I've defined a function below that checks whether you've included "s3://" in the input, and if not, I want it to throw an error.

When I test this out and omit the "s3://" in the input, no error is thrown. What am I doing wrong?

Form class:

from flask_wtf import FlaskForm
from wtforms import StringField, TextField, SubmitField, IntegerField, SelectField, validators
from wtforms.validators import ValidationError
import boto3

# CUSTOM VALIDATOR
def is_s3_uri(form, field):
if "s3://" not in field.data:
raise ValidationError('Bucket name must contain full path. Missing "s3://".')

class InputForm(FlaskForm):

input_uri = StringField('INPUT BUCKET', validators=[validators.required(), is_s3_uri])
output_uri = StringField('OUTPUT BUCKET', validators=[validators.required(), is_s3_uri])


HTML:

<div class="tab">
<h3>File Locations:</h3>
<div class="form-group required">
form.input_uri.label : form.input_uri(placeholder="(e.g. s3://pipeline-run/fastqs/)...", oninput=", this.className = ''")
</div>
% if form.input_uri.errors %
<ul class="errors">% for error in form.input_uri.errors %<li> error </li>% endfor %</ul>
% endif %
<div class="form-group required">
form.output_uri.label : form.output_uri(placeholder="(e.g. s3://pipeline-run/results/)...", oninput="this.className = ''")
</div>
% if form.input_uri.errors %
<ul class="errors">% for error in form.output_uri.errors %<li> error </li>% endfor %</ul>
% endif %
</div>


UPDATE:

I also tried adding a built-in validator (e.g. with Length(min=6, max=120)), but that doesn't get enforced either.

Length(min=6, max=120))

stack_name = StringField('STACK NAME', validators=[Length(min=4, max=120), DataRequired()])


UPDATE 2:

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

INPUT_URI = ''
OUTPUT_URI = ''

form = InputForm(request.form)

if request.method == 'POST':
if form.validate_on_submit():
INPUT_URI = request.form['input_uri']
OUTPUT_URI = request.form['output_uri']

# process info

else:
flash('Invalid params. Please re-try.', 'danger')
return redirect(request.path)

return render_template('pipeline-alt.html',
title='Pipeline Input',
form=form)


UPDATE 3:
Using the Jquery Form Validation Plugin

HTML:

<div class="form-group required">
form.input_uri.label : form.input_uri(placeholder="(e.g. s3://pipeline-run/fastqs/)...", oninput=", this.className = ''", name="input_uri")
</div>


JQuery:

<script>

$(document).ready(function ()

$('#regForm').validate( // initialize the plugin
rules:
input_uri:
required: true,
minlength: 4

,
submitHandler: function (form) // for demo
alert('valid form submitted'); // for demo
return false; // for demo

);

);

</script>


Result: TypeError: html_params() got multiple values for keyword argument 'name'

TypeError: html_params() got multiple values for keyword argument 'name'

1 Answer
1

Are you validating your form on submit? You didn't post enough code but I will try to help.

In the view that renders you should use form.validate_on_submit() in order for you form to get validated. I don't see your entire form code in the HTML you posted and if this is it, then you are missing a submit button that will send the form to the server for validation.

form.validate_on_submit()

Please post your view (that renders the form) code

Your form should use POST in the method for the example below.
An example of what your view that handles the form should llok like with form.validate_on_submit()

POST

form.validate_on_submit()

from flask import request
@app.route('/form_route', methods=['GET', 'POST'])
def form_route():
form = YourFormClass()
if request.method == 'POST':
if form.validate_on_submit():
# validation will be triggered from the if statement and if it validates, it will enter this if block
# perform actions if the form is valid
else:
# do somthing if the form is not valid
return render_template(form=form)


validate_on_submit()

UPDATE 3

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