Multiple forms in a single page using flask and WTForms

I have multiple form on the same page that send post request to same handler in flask.

I am generating forms using wtforms.

what is the best way to identify which form is submitted ?

I am currently using action="?form=oneform". I think there should be some better method to achieve the same?

The solution above have a validation bug, when one form cause a validation error, both forms display an error message. I change the order of if to solve this problem.

First, define your multiple SubmitField with different names, like this:

class Form1(Form):
    name = StringField('name')
    submit1 = SubmitField('submit')

class Form2(Form):
    name = StringField('name')
    submit2 = SubmitField('submit')

....

Then add a filter in view.py:

....
form1 = Form1()
form2 = Form2()
....

if form1.submit1.data and form1.validate(): # notice the order 
....
if form2.submit2.data and form2.validate(): # notice the order 
....

Now the problem was solved.

If you want to dive into it, then continue read.

Here is validate_on_submit():

def validate_on_submit(self):
    """
    Checks if form has been submitted and if so runs validate. This is
    a shortcut, equivalent to ``form.is_submitted() and form.validate()``
    """
    return self.is_submitted() and self.validate()

And here is is_submitted():

def is_submitted():
    """Consider the form submitted if there is an active request and
    the method is ``POST``, ``PUT``, ``PATCH``, or ``DELETE``.
    """
    return _is_submitted()  # bool(request) and request.method in SUBMIT_METHODS
    

When you call form.validate_on_submit(), it check if form is submitted by the HTTP method no matter which submit button was clicked. So the little trick above is just add a filter (to check if submit has data, i.e., form1.submit1.data).

Besides, we change the order of if, so when we click one submit, it only call validate() to this form, preventing the validation error for both form.

The story isn't over yet. Here is .data:

@property
def data(self):
    return dict((name, f.data) for name, f in iteritems(self._fields))

It return a dict with field name(key) and field data(value), however, our two form submit button has same name submit(key)!

When we click the first submit button(in form1), the call from form1.submit1.data return a dict like this:

temp = {'submit': True}

There is no doubt when we call if form1.submit.data:, it return True.

When we click the second submit button(in form2), the call to .data in if form1.submit.data: add a key-value in dict first, then the call from if form2.submit.data: add another key-value, in the end, the dict will like this:

temp = {'submit': False, 'submit': True}

Now we call if form1.submit.data:, it return True, even if the submit button we clicked was in form2.

That's why we need to define this two SubmitField with different names. By the way, thanks for reading(to here)!

Update

There is another way to handle multiple forms on one page. You can use multiple views to handle forms. For example:

...
@app.route('/')
def index():
    register_form = RegisterForm()
    login_form = LoginForm()
    return render_template('index.html', register_form=register_form, login_form=login_form)

@app.route('/register', methods=['POST'])
def register():
    register_form = RegisterForm()
    login_form = LoginForm()
    
    if register_form.validate_on_submit():
        ...  # handle the register form
    # render the same template to pass the error message
    # or pass `form.errors` with `flash()` or `session` then redirect to /
    return render_template('index.html', register_form=register_form, login_form=login_form)
    

@app.route('/login', methods=['POST'])
def login():
    register_form = RegisterForm()
    login_form = LoginForm()
    
    if login_form.validate_on_submit():
        ...  # handle the login form
    # render the same template to pass the error message
    # or pass `form.errors` with `flash()` or `session` then redirect to /
    return render_template('index.html', register_form=register_form, login_form=login_form)
    

In the template (index.html), you need to render both forms and set the action attribute to target view:

<h1>Register</h1>
<form action="{{ url_for('register') }}" method="post">
    {{ register_form.username }}
    {{ register_form.password }}
    {{ register_form.email }}
</form>

<h1>Login</h1>
<form action="{{ url_for('login') }}" method="post">
    {{ login_form.username }}
    {{ login_form.password }}
</form>

I've been using a combination of two flask snippets. The first adds a prefix to a form and then you check for the prefix with validate_on_submit(). I use also Louis Roché's template to determine what buttons are pushed in a form.

To quote Dan Jacob:

Example:

form1 = FormA(prefix="form1")
form2 = FormB(prefix="form2")
form3 = FormC(prefix="form3")

Then, add a hidden field (or just check a submit field):

if form1.validate_on_submit() and form1.submit.data:

To quote Louis Roché's:

I have in my template :

<input type="submit" name="btn" value="Save">
<input type="submit" name="btn" value="Cancel">

And to figure out which button was passed server side I have in my views.py file:

if request.form['btn'] == 'Save':
    something0
else:
    something1

A simple way is to have different names for different submit fields. For an example:

forms.py：

class Login(Form):

    ...
    login = SubmitField('Login')


class Register(Form):

    ...
    register = SubmitField('Register')

views.py:

@main.route('/')
def index():

    login_form = Login()
    register_form = Register()


    if login_form.validate_on_submit() and login_form.login.data:
        print "Login form is submitted"

    elif register_form.validate_on_submit() and register_form.register.data:
        print "Register form is submitted"
    
    ...

As the other answers, I also assign a unique name for each submit button, for each form on the page.

Then, the flask web action looks like below - note the formdata and obj parameters, which help to init / preserve the form fields accordingly:

@bp.route('/do-stuff', methods=['GET', 'POST'])
def do_stuff():
    result = None

    form_1 = None
    form_2 = None
    form_3 = None

    if "submit_1" in request.form:
        form_1 = Form1()
        result = do_1(form_1)
    elif "submit_2" in request.form:
        form_2 = Form2()
        result = do_2(form_2)
    elif "submit_3" in request.form:
        form_3 = Form3()
        result = do_3(form_3)

    if result is not None:
        return result

    # Pre-populate not submitted forms with default data.
    # For the submitted form, leave the fields as they were.
    
    if form_1 is None:
        form_1 = Form1(formdata=None, obj=...)
    if form_2 is None:
        form_2 = Form2(formdata=None, obj=...)
    if form_3 is None:
        form_3 = Form3(formdata=None, obj=...)

    return render_template("page.html", f1=form_1, f2=form_2, f3=form_3)


def do_1(form):
    if form.validate_on_submit():
        flash("Success 1")
        return redirect(url_for(".do-stuff"))


def do_2(form):
    if form.validate_on_submit():
        flash("Success 2")
        return redirect(url_for(".do-stuff"))

def do_3(form):
    if form.validate_on_submit():
        flash("Success 3")
        return redirect(url_for(".do-stuff"))

Well here is a simple trick

Assume you Have

> Form1, Form2, and index

---

Form1  <form method="post" action="{{ url_for('index',formid=1) }}">

Form2  <form  method="post" action="{{ url_for('index',formid=2) }}">

---

Now In index

@bp.route('/index', methods=['GET', 'POST'])
def index():
    formid = request.args.get('formid', 1, type=int)
    if formremote.validate_on_submit() and formid== 1:
        return "Form One"
    if form.validate_on_submit() and formid== 2:
        return "Form Two"

I haven't used WTForms but should work regardless. This is a very quick and simple answer; all you need to do is use different values for the submit button. You can then just do a different def based on each.

In index.html:

    <div>
        <form action="{{ url_for('do_stuff')}}" method="POST">
            <h1>Plus</h1>
            <input type = "number" id = "add_num1" name = "add_num1" required><label>Number 1</label><br>
            <input type = "number" id = "add_num2" name = "add_num2" required><label>Number 2</label><br>
            <input type = "submit" value = "submit_add" name = "submit" ><br>
        </form>
        <p>Answer: {{ add }}</p>
    </div>
    
    <div>
        <form action="{{ url_for('do_stuff')}}" method="POST">
            <h1>Minus</h1>
            <input type = "number" id = "min_num1" name = "min_num1" required><label>Number 1</label><br>
            <input type = "number" id = "min_num2" name = "min_num2" required><label>Number 2</label><br>
            <input type = "submit" value = "submit_min" name = "submit"><br>
        </form>
        <p>Answer: {{ minus }}</p>
    </div>

in app.py:

@app.route('/',methods=["POST"])
def do_stuff():
    if request.method == 'POST':
        add = ""
        minus = ""
        if request.form['submit'] == 'submit_add':
            num1 = request.form['add_num1']
            num2 = request.form['add_num2']
            add = int(num1) + int(num2)
        
        if request.form['submit'] == 'submit_min':
            num1 = request.form['min_num1']
            num2 = request.form['min_num2']
            minus = int(num1) - int(num2)
    return render_template('index.html', add = add, minus = minus)

Example: Multiple WTForm in single html page

app.py

"""
Purpose Create multiple form on single html page.

Here we are having tow forms first is Employee_Info and CompanyDetails
"""
from flask import Flask, render_template, request
from flask_wtf import FlaskForm
from wtforms import StringField, IntegerField, FloatField, validators
from wtforms.validators import InputRequired

app = Flask(__name__)
app.config['SECRET_KEY'] = 'Thisisasecret'

class EmployeeInfo(FlaskForm):
	"""
	EmployeeInfo class will have Name,Dept
	"""
	fullName = StringField('Full Name',[validators.InputRequired()])
	dept = StringField('Department',[validators.InputRequired()])

class CompanyDetails(FlaskForm):
	"""
	CompanyDetails will have yearOfExp. 
	"""
	yearsOfExp = IntegerField('Year of Experiece',[validators.InputRequired()])	


@app.route('/', methods = ['GET','POST'] )
def index():
	"""
	View will render index.html page.
	If form is validated then showData.html will load the employee or company data.
	"""
	companydetails = CompanyDetails()
	employeeInfo = EmployeeInfo()
	
	if companydetails.validate_on_submit():
		return render_template('showData.html', form = companydetails)
	
	if employeeInfo.validate_on_submit():
		return render_template('showData.html', form1 = employeeInfo)	

	return render_template('index.html',form1 = employeeInfo, form = companydetails)

if __name__ == '__main__':
	app.run(debug= True, port =8092)

templates/index.html

<html>
	<head>
	</head>
	<body>	
		<h4> Company Details </h4>
	
		<form method="POST" action="{{url_for('index')}}">
		
			{{ form.csrf_token }}

			{{ form.yearsOfExp.label }} {{ form.yearsOfExp }}		

			<input type="submit" value="Submit">
		</form>

		<hr>
		<h4> Employee Form </h4>
	
		<form method="POST" action="{{url_for('index')}}" >

			{{ form1.csrf_token }}

			{{ form1.fullName.label }} {{ form1.fullName }}

			{{ form1.dept.label }} {{ form1.dept }}

			<input type="submit" value="Submit">
		</form>
	</body>
</html>

showData.html

<html>
	<head> 
	</head> 
	<body>
		{% if form1 %}
		<h2> Employee Details </h2>
			{{ form1.fullName.data }}
			{{ form1.dept.data }}
		{% endif %}
		{% if form %}
			<h2> Company Details </h2>
				{{ form.yearsOfExp.data }}		
		{% endif %}		
	</body>
</html>

I normally use a hidden tag that works as an identifier.

Here is an example:

class Form1(Form):
    identifier = StringField()
    name = StringField('name')
    submit = SubmitField('submit')

class Form2(Form):
    identifier = StringField()
    name = StringField('name')
    submit = SubmitField('submit')

Then you can add a filter in view.py:

....
form1 = Form1()
form2 = Form2()
....

if form1.identifier.data == 'FORM1' and form1.validate_on_submit():
....
if form2.identifier.data == 'FORM2' and form2.validate_on_submit():
....

and finally in the HTML:

<form method="POST">
  {{ form1.indentifier(hidden=True, value='FORM1') }}
</form>
<form method="POST">
  {{ form2.indentifier(hidden=True, value='FORM2') }}
</form>

If you do it like this in the if statement it will check what was the identifier and if its equal it will run the form stuff you have in your code.