Wtform nested fields not populated with populate_obj - flask

Question

So I have this DemandeForm with nested FormField:
AdressePrivee = FormField(AdresseForm, default=AdressePrivee())
with Demande model:
AdressePrivee = db.relationship(AdressePrivee, backref='Demande', lazy=False, uselist=False)
I have nested fields submitted in the HTML form:
AdressePrivee-RueEtNumero: Boulevard Bonivard 11
AdressePrivee-ComplementNom:
AdressePrivee-ComplementAdresse:
AdressePrivee-CasePostale: 01420
AdressePrivee-NPA:
AdressePrivee-Localite: Seyssel
AdressePrivee-Pays: 2
And I call it with:
form = DemandeForm(data=request.form)
if form.validate():
form.populate_obj(demande) # Here, demande.AdressePrivee should be populated
db.session.add(demande)
db.session.commit()
flash('Enregistré', 'success')
return redirect(url_for('main.index'))
But if I print it there, all entries are set to None, as if demande.AdressePrivee is only equal to AdressePrivee() empty object (log: <AdressePrivee None None None>), while FormFields should be set, with the nested fields logic, shouldn't they?
Am I missing something?

Answer 1

I think you can't use the constructor directly, you should use a factory.
AdressePrivee = FormField(AdresseForm, default=lambda: AdressePrivee())
I also think the attribute for transferring the form data of the request is called "formdata" not "data".
form = DemandeForm(formdata=request.form)
In the following a small example that worked for me.
class Address(db.Model):
id = db.Column(db.Integer, primary_key=True)
street = db.Column(db.String, nullable=False)
class Inquiry(db.Model):
id = db.Column(db.Integer, primary_key=True)
title = db.Column(db.String, nullable=False)
address_id = db.Column(db.Integer,
db.ForeignKey('address.id', ondelete='cascade'),
nullable=False
)
address = db.relationship('Address', backref='inquiry', lazy=False, uselist=False)
class AddressForm(FlaskForm):
street = StringField('street', validators=[DataRequired()])
def __init__(self, csrf_enabled=False, *args, **kwargs):
super().__init__(csrf_enabled=csrf_enabled, *args, **kwargs)
class InquiryForm(FlaskForm):
title = StringField('title', validators=[DataRequired()])
address = FormField(AddressForm, default=lambda: Address())
#app.route('/new', methods=['GET', 'POST'])
def create():
item = Inquiry()
form = InquiryForm(request.form)
if form.validate_on_submit():
form.populate_obj(item)
db.session.add(item)
db.session.commit()
items = Inquiry.query.all()
return render_template('create.html', **locals())
I wish you every success in implementing your project and hope I was able to help you.