Flask-RESTful with Flask-WTF forms integration

Question

I am using Flask with Flask-RESTful. I have POST method which gets data and I need to apply validation checks on it. My question is can i use Flask-WTF with that like Django-Forms for handling validations and checks?

What technique do you prefer for the scenario for Signup where i need to check if an Email already exists in the system?

Answer 1

The reqparse module of Flask-RESTful provides what you are looking for. By defining your own type of input fields, you can perform some validation operations. Here is an example from scratch:

from flask import Flask
from flask.ext.restful import Api, Resource, reqparse

app = Flask(__name__)
api = Api(app)


def is_email_valid(address):
    # Check if the e-mail address already exists in database.
    return True  # or False

def email(value):
    if not is_email_valid(value):
        raise ValueError("The e-mail address {} is already taken.".format(value))

    return value

class Users(Resource):
    parser = reqparse.RequestParser()
    parser.add_argument('email', type=email, help='Signup email')

    def post(self):
        args = self.parser.parse_args()
        # Create the new user with args.items()
        return "user representation", 201


api.add_resource(Users, '/users')


if __name__ == '__main__':
    app.run(debug=True)

If an argument fails to pass validation, the parser automatically responds with a 400 Bad Request.

You can find more information in the documentation of Flask-RESTful.

Similarly, you can do this with WTForms :

from flask import Flask, request
from flask.ext.restful import Api, Resource, abort
from wtforms import Form, fields, validators

app = Flask(__name__)
api = Api(app)


# WTForms
def is_email_valid(address):
    # Check if the e-mail address already exists in database.
    return True  # or False

def user_email(form, field):
    if not is_email_valid(field.data):
        raise validators.ValidationError("The e-mail address {} is already taken.".format(field.data))

class UserForm(Form):
    email = fields.StringField('Email', [validators.Email(), user_email])


# Flask-RESTful
class Users(Resource):
    def post(self):
        form = UserForm(data=request.get_json())
        if form.validate():
            # Create the new user with form.populate_obj()
            pass
        else:
            abort(400)
        return "user representation", 201


api.add_resource(Users, '/users')


if __name__ == '__main__':
    app.run(debug=True)

However, even with the WTForms implementation, you have to define your form's fields unless you use a compatible ORM. For example, some extensions of WTForms generate forms from models similarly to how it can be done for Django ORM models.