Develop Reference

Flask redirects to wrong view when redirecting to index

I keep running into this strange issue that I can't seem to figure out a solution for. I cannot copy and show all of my code in it's entirety here, but I will try to outline the general structure of my flask app to present my issue.
(Let's ignore all of the content in the /static folder and my helper modules)
I have 3 main views, let's call them viewA, viewB, and index:
viewA.html
viewB.html
index.html
viewA and viewB both display two forms, but with different content (i.e. viewA displays form1 & form2, and viewB also displays form1 & form2).
A simplified version of my script code is as follows:
#imports
from flask import Flask, render_template, session, redirect, url_for, request
from flask_wtf import FlaskForm
#etc. etc.
app = Flask(__name__)
app.config['SECRET_KEY'] = 'blah blah blah'
manager = Manager(app)
bootstrap = Bootstrap(app)
moment = Moment(app)
class FormOne(FlaskForm):
sample_field = StringField('Sample Field:')
class FormTwo(FlaskForm):
other_field = StringField('Other Field:', validators=[Required()])
submit = SubmitField('Submit')
class UploadToA(FlaskForm):
content= StringField('Content to send to view A:', validators=[Required()])
submit = SubmitField('Submit')
class UploadToB(FlaskForm):
content= StringField('Content to send to view A:', validators=[Required()])
submit = SubmitField('Submit')
#app.route('/ViewA', methods=['GET', 'POST'])
def view_a():
"""
A lot of data manipulation
"""
form1 = FormOne()
form2 = FormTwo()
if request.method == 'GET':
"""
populate forms with content
"""
if request.method == 'POST':
if form2.validate_on_submit();
"""
clear session variables
"""
return redirect(url_for('index'), code=302)
return render_template('viewA.html', form1=form1, form2=form2)
#app.route('/ViewB', methods=['GET', 'POST'])
def view_b():
"""
A lot of data manipulation
"""
form1 = FormOne()
form2 = FormTwo()
if request.method == 'GET':
"""
populate forms with content
"""
if request.method == 'POST':
if form2.validate_on_submit();
"""
clear session variables
"""
return redirect(url_for('index'), code=302)
return render_template('viewB.html', form1=form1, form2=form2)
#app.route('/', methods=['GET', 'POST'])
def index():
"""
Some data manipulation
"""
formA = UploadToA()
formB = UploadToB()
if formA.validate_on_submit()':
"""
pull content from form A
create some session variables
"""
return redirect(url_for('view_a'))
if formB.validate_on_submit()':
"""
pull content from form B
create some session variables
"""
return redirect(url_for('view_b'))
return render_template('index.html', formA=formA, formB=formB)
if __name__ == '__main__':
manager.run()
Now the issue at hand I am having here is that for some strange reason when I'm in 'viewA.html' and I submit my form, I SHOULD be redirected back to 'index.html' but for some strange reason it redirects me to 'viewB.html'. Furthermore, the opposite also holds true: when i'm in 'viewB.html' and I submit my form, I SHOULD also be redirected back to 'index.html' but it redirects me to 'viewA.html'. Yet, if I am in either viewA or viewB, I have no issues of going back to the index view if I manually enter the url into my browser.
Any ideas as to why I might be running into this issue?
Thanks in advance :)

I have finally figured out the source of my problem. It turns out that in my 'viewA.html' template file, I had the following in my < form > tag:
<form class="form form-horizontal" method="post" role="form" action="{{url_for('index')}}">
And the problem all lies in that last part:
action="{{url_for('index')}}"
As a result, everytime I would submit form2 in viewA.html it would create a post request for my index page rather than a post request for the viewA.html page (which caused a redirect to the wrong view). Thus, by simply removing the action attribute (action="{{url_for('index')}}"), I was able to solve my problem!

Since the full code isn't here, I can't confirm this for sure, but what I think is happening is this:
You open form A
You submit form A
It sends a redirect to /index
It sends a redirect to /FormB
if formB.validate_on_submit():
return redirect(url_for('view_b'))
This is probably sending a redirect to View B. Try changing that last line to something like return something_else and seeing if it sends that after submitting form A.

How to rewrite this Flask view function to follow the post/redirect/get pattern?

I have a small log browser. It retrieves and displays a list of previously logged records depending on user's input. It does not update anything.
The code is very simple and is working fine. This is a simplified version:
#app.route('/log', methods=['GET', 'POST'])
def log():
form = LogForm()
if form.validate_on_submit():
args = parse(form)
return render_template('log.html', form=form, log=getlog(*args))
return render_template('log.html', form=form)
However it does not follow the post/redirect/get pattern and I want to fix this.
Where should I store the posted data (i.e. the args) between post and get? What is the standard or recommended approach? Should I set a cookie? Should I use flask.session object, create a cache there? Could you please point me in the right direction? Most of the time I'm writing backends...
UPDATE:
I'm posting the resulting code.
#app.route('/log', methods=['POST'])
def log_post():
form = LogForm()
if form.validate_on_submit():
session['logformdata'] = form.data
return redirect(url_for('log'))
# either flash errors here or display them in the template
return render_template('log.html', form=form)
#app.route('/log', methods=['GET'])
def log():
try:
formdata = session.pop('logformdata')
except KeyError:
return render_template('log.html', form=LogForm())
args = parse(formdata)
log = getlog(args)
return render_template('log.html', form=LogForm(data=formdata), log=log)

So, ultimately the post/redirect/get pattern protects against submitting form data more than once. Since your POST here is not actually making any database changes the approach you're using seems fine. Typically in the pattern the POST makes a change to underlying data structure (e.g. UPDATE/INSERT/DELETE), then on the redirect you query the updated data (SELECT) so typically you don't need to "store" anything in between the redirect and get.
With all the being said my approach for this would be to use the Flask session object, which is a cookie that Flask manages for you. You could do something like this:
#app.route('/log', methods=['GET', 'POST'])
def log():
form = LogForm()
if form.validate_on_submit():
args = parse(form)
session['log'] = getlog(*args)
return redirect(url_for('log'))
saved = session.pop('log', None)
return render_template('log.html', form=form, log=saved)
Also, to use session, you must have a secret_key set as part of you application configuration.
Flask Session API
UPDATE 1/9/16
Per ThiefMaster's comment, re-arranged the order of logic here to allow use of WTForms validation methods for invalid form submissions so invalid form submissions are not lost.

The common way to do P/R/G in Flask is this:
#app.route('/log', methods=('GET', 'POST'))
def log():
form = LogForm()
if form.validate_on_submit():
# process the form data
# you can flash() a message here or add something to the session
return redirect(url_for('log'))
# this code is reached when the form was not submitted or failed to validate
# if you add something to the session in case of successful submission, try
# popping it here and pass it to the template
return render_template('log.html', form=form)
By staying on the POSTed page in case the form failed to validate WTForms prefills the fields with the data entered by the user and you can show the errors of each field during form rendering (usually people write some Jinja macros to render a WTForm easily)

Clear valid form after it is submitted

I want to reset the form after it validates. Currently the form will still show the previous data after it is submitted and valid. Basically, I want the form to go back to the original state with all fields clean. What is the correct to do this?
#mod.route('/', methods=['GET', 'POST'])
def home():
form = NewRegistration()
if form.validate_on_submit():
#save in db
flash(gettext(u'Thanks for the registration.'))
return render_template("users/registration.html", form=form)

The issue is that you're always rendering the form with whatever data was passed in, even if that data validated and was handled. In addition, the browser stores the state of the last request, so if you refresh the page at this point the browser will re-submit the form.
After handling a successful form request, redirect to the page to get a fresh state.
#app.route('/register', methods=['GET', 'POST'])
def register():
form = RegistrationForm()
if form.validate_on_submit():
# do stuff with valid form
# then redirect to "end" the form
return redirect(url_for('register'))
# initial get or form didn't validate
return render_template('register.html', form=form)

davidism answer is correct.
But once I had to reload a form with only a few fields that had to be resetted.
So, I did this, maybe it's not the cleanest way but it worked for me:
form = MyForm()
if form.validate_on_submit():
# save all my data...
myvar1 = form.field1.data
myvar2 = form.field2.data
# etc...
# at first GET and at every reload, this is what gets executed:
form.field1.data = "" # this is the field that must be empty at reload
form.field2.data = someobject # this is a field that must be filled with some value that I know
return render_template('mypage.html', form=form)

You can clear a form by passing formdata=None
#mod.route('/', methods=['GET', 'POST'])
def home():
form = NewRegistration()
if form.validate_on_submit():
#save in db
######### Recreate form with no data #######
form = NewRegistration(formdata=None)
flash(gettext(u'Thanks for the registration.'))
return render_template("users/registration.html", form=form)

you can also return new form object using render_template if form does not validates you can also pass message
#mod.route('/', methods=['GET', 'POST'])
def home():
form = NewRegistration()
if form.validate_on_submit():
#save in db
return render_template("user/registration.html", form = NewRegistration())
return render_template("users/registration.html", form=form)

How do different Form objects communicate in Flask-wtforms?

A typical view is something like
#app.route('/login', methods=['GET', 'POST'])
def login():
form = LoginForm()
if form.validate_on_submit():
# do stufff
return redirect(url_for('somewhere_else', param=param))
return render_template('login.html', form=form)
What I'm confused about: when the login() view is called, isn't a new LoginForm() instantiated with form = LoginForm()? How does this brand new form ever validate_on_submit()?

It's addressed in the first page of the quick-start guide in the documentation:
Note that you don’t have to pass request.form to Flask-WTF; it will load automatically. And the convenience validate_on_submit will check if it is a POST request and if it is valid.
So when you instantiate the form, it'll automatically load in the existing request if it can.

Look at the source code of flask-wtf (I removed unrelated fragments and added comments):
class Form(SecureForm):
# ...
def __init__(self, formdata=_Auto, obj=None, prefix='', csrf_context=None,
secret_key=None, csrf_enabled=None, *args, **kwargs):
# ...
if formdata is _Auto:
if self.is_submitted():
formdata = request.form # !!! LOOK HERE !!!
if request.files:
formdata = formdata.copy()
formdata.update(request.files)
elif request.json:
formdata = werkzeug.datastructures.MultiDict(request.json)
else:
formdata = None
# ...
So, if you don't pass formdata explicitly to form's constructor and current request "is submitted" (the method is either PUT or POST), it uses the request.form.

Flask login_required + next url params

I have a protected view in my app which just accepts POST requests.
#app.route("/booking", methods=("POST", ))
#login_required
def booking():
arg1 = request.form.get("arg1")
arg2 = request.form.get("arg2")
When an unauthorized user tries to access this view, I want them to
login and then be redirected here.
Right now, my login view looks like this:
#app.route("/login", methods=("GET", "POST"))
#login_required
def login():
do_login()
return redirect(request.args.get('next') or url_for('home'))
So what ends up happening is a POST request to /booking (which is the
"next" parameter) and I get a NOT ALLOWED error.
The problem is that login() makes a GET request to booking(). I can
get around that, but I am not sure how to retrieve the original POST
form arguments from /booking? Any ideas to get round that?

I would solve this by pulling the data and putting it in the session. You can remove the #login_required decorator and check this in the function using current_user.is_authorized. See Flask Sessions and Flask Login.
Something like this might work for you, I didn't test it:
from flask import session
from flask_login import current_user
#app.route("/booking", methods=("POST", ))
def booking():
if not 'arg1' in session.keys() and not 'arg2' in session.keys():
session['arg1'] = request.form.get("arg1")
session['arg2'] = request.form.get("arg2")
# Now the data will persist in the session
if current_user.is_authorized:
# Do what you need...
else:
# Redirect to login, session will persist

Why would you only use POST in the booking view ? You are probably rendering a form which should also allow GET.
#app.route("/booking", methods=['GET','POST'])
#login_required
def booking():
# render the form. something like
form = BookingForm()
# Check if POST
if request.method == 'POST':
# process the form now and do whatever you need.
return redirect(url_for('index'))
# code below will run if not POST. You should render the template here
return render_templte('booking.html')