WTForms: populate form with data if data exists

Question

I have the following Flask-WTF form:

class PersonForm(FlaskForm):
    name = StringField('Name', validators=[DataRequired()])
    age = IntegerField('Age', validators=[NumberRange(min=0)], render_kw={'type': 'number'})
    educated = BooleanField('Educated', render_kw={'type': 'checkbox'})

I know I can pre-populate the form by passing values into the form like so:

form = PersonForm(name='Johnny', age=25, educated=True)

I've noticed there's a better way to do this by injecting an object into the form (references here and here). I've tried the following, however, it doesn't work. Where am I going wrong (is the object supposed to be something other than a dictionary)?

person = {'name': 'Johnny', 'age': 25, 'educated'=True}
form = PersonForm(obj=person)

Note these pre-populated values come from a database. Some values are defined while some aren't. For example, another "person" may look like {'name': 'Jessica', 'educated': True} (the age field will be empty in this case).

Yeah, it needs to be a MultiDict. This is what the flask request post data comes back as. It's intended to be used with post data in the flask request. — Artagel
– Artagel, Commented Mar 23, 2017 at 18:53
How can I create a MultDict from data I retrieve from a database? — Johnny Metz
– Johnny Metz, Commented Mar 23, 2017 at 19:54

Iron Fist · Accepted Answer · 2017-03-24 19:03:28Z

12

I think you want to use the data parameter instead, as mentioned in this documentation:

The Form class

class wtforms.form.Form

Declarative Form base class. Construction
__init__(formdata=None, obj=None, prefix='', data=None, meta=None, **kwargs)
    Parameters:   
...

data – Accept a dictionary of data. This is only used if formdata and obj are not present. ...

Demonstration:

>>> from wtforms import Form, StringField, validators
>>>
>>> class UsernameForm(Form):
    username = StringField('Username', [validators.Length(min=5)], default=u'test')
    email = StringField('Email', [validators.email(message='Check your email')], default=u'[email protected]')
>>>
>>> person = {'username': 'Johnny', 'email': '[email protected]'}
>>>
>>> form = UsernameForm(data=person)
>>> 
>>> form.username.data
'Johnny'
>>> 
>>> form.email.data
'[email protected]'

It does work with the formdata parameter as well, but you will have to pass a MultiDict object:

>>> from werkzeug.datastructures import MultiDict
>>> 
>>> b = MultiDict(person)
>>> 
>>> b
MultiDict([('email', '[email protected]'), ('username', 'Johnny')])
>>> 
>>> 
>>> form2 = UsernameForm(formdata=b)
>>> form2.username.data
'Johnny'
>>> form2.email.data
'[email protected]'
>>>

Also with **kwargs passed as a regular dictionary:

>> form3 = UsernameForm(**person)
>>> 
>>> form3.username.data
'Johnny'
>>> 
>>> form3.email.data
'[email protected]'

EDIT: in reply to OP's comment concerning the use of obj parameters and quoting from docs:

 __init__(formdata=None, obj=None, prefix='', data=None, meta=None, **kwargs)
Parameters:
...

obj – If formdata is empty or not provided, this object is checked for attributes matching form field names, which will be used for field values.

...

That means you need to pass in an object with attribute names same as your forms' attribute name, as follows:

>>> class Person:
        username = 'Johny'
        email = '[email protected]'

>>> 
>>> form = UsernameForm(obj=Person)
>>> 
>>> form.data
{'email': '[email protected]', 'username': 'Johny'}

edited Mar 24, 2017 at 19:03

answered Mar 24, 2017 at 11:14

Iron Fist

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4 Comments

Johnny Metz Over a year ago

Awesome answer thank you. So what is the obj parameter used for?

Johnny Metz Over a year ago

Super helpful! Thanks

Iron Fist Over a year ago

@jcmetz21...No pblm :)

Nurhun Over a year ago

@IronFist what for prepopulating fieldlist ? how to access each entry and set it's value ?

Rob Surf · Accepted Answer · 2023-11-20 15:36:17Z

I used a session variable to pass data from my form on POST back to my template on GET to have form user filled values rendered in case of error on Post or user page refresh - to not clear the form and annoy user.

I had to directly pass the full form.request back to the template and index back out values from that dict for prefilling data in my html template as I have no class defining the fields of my form in my python Flask App. Other cleaner answers make use of a form class and pass that to the html - I'm not so well setup ;)

Relevant Code below - leaving out the unrelated bits in app.py:

if ( request.method == 'POST'):
    session['last_request_data']= request.form
if (form_error):
    return render_template('home.html', prefill_data=session['last_request_data'])

if ( request.method == 'GET'):

if ('last_request_data' in session): 
    print("Prefill form with last data from the session")      
    return render_template('home.html', prefill_data=session['last_request_data'])
else:
    print("Frist time page load - no data to prefill - render empty form")   
    return render_template('home.html')

And then in the html template - I have to check if there was any prefill data was passed each time I try to prefill values using the keys from the form ...

            <input type="text" name="player1name" {% if prefill_data %} value="{{ prefill_data.get("player1name") }}"{% endif %}/>

Artagel · Accepted Answer · 2017-03-23 19:58:50Z

0

You need a MultiDict

>>> a
{'hello': 'data', 'more': 'data'}
>>> from werkzeug.datastructures import MultiDict
>>> b=MultiDict(a)
>>> b
MultiDict([('hello', 'data'), ('more', 'data')])
>>>

answered Mar 23, 2017 at 19:58

Artagel

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4 Comments

Johnny Metz Over a year ago

I just tried passing this MultiDict to the form but no luck: form = PersonForm(obj=MultiDict(person))

Artagel Over a year ago

Is your db data a dictionary?

Artagel Over a year ago

Try: form = PersonForm(); form.populate_obj(req)

Johnny Metz Over a year ago

That didn't seem to work either. I'm using mongodb so yes, the data is retrieved as a python dictionary.

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