WTForms BooleanField treats JSON false value as true

Question

I'm using wtforms to handle data from my post requests. One certain post requests sends a variety of data including a boolean value.

My form looks like this:

class EditFileForm(Form):
    title = StringField('title')
    shared = BooleanField('shared')
    fileID = IntegerField('fileID')
    userID = IntegerField('userID')

I can see that when I receive the request the data looks like this:

data = MultiDict(mapping=request.json)
print(data)
>>MultiDict([(u'shared', False), (u'title', u'File5'), (u'userID', 1), (u'fileID', 16)])

You can see the boolean field is "false", and printing the raw data shows that too However, when I print the actual form field I get true.

print(form.shared.raw_data)
[False]
print(form.shared.data)
True

I read that WTForms might not know how to handle false boolean values. What is the proper way of doing this? Using an IntegerField instead?

I have another form with a booleanfield that is handling false boolean values from my postgres database just fine.

Answer 1

WTForms is not really meant to work with JSON data. In this case, BooleanField checks that the value it received is in field.false_values, which defaults to ('false', ''). The False object is not in there, so it's considered true.

You can pass a different set of false_values to the field.

BooleanField(false_values={False, 'false', ''})

Or patch it for all instances by placing this somewhere before the field is used for the first time.

BooleanField.false_values = {False, 'false', ''}

You may better off using a serialization library such as Marshmallow to handle JSON data.