on_form_prefill delete all fields values if it executes form.process

Question

I want to override the form of the Matriline model shown below.

First I add an extra field clan, and in on_form_prefill I reset this field's choices and default (just testing).

Without calling form.process the choices are set to my new options, but the default option is not selected.

If calling form.process the choices are set to my new options and the default option is selected, but all the other fields are deleted.

Anybody can help?

views.py

class MatrilineAdmin(sqla.ModelView):

    form_extra_fields = {
        'clan': SelectField('Clan',
            coerce=int,
            choices=[ (c.id, c.name) for c in Clan.query.all()])
    }
    create_template = 'admin/create.html'
    edit_template = 'admin/edit.html'

    def on_form_prefill(self, form, id):
        form.clan.choices = [(1, "first"),(2,"second")]
        form.clan.default = 2
        form.process() # if commented, set choices but does not set default
                       # else set choices and default but delete all the other fields values (name and pod_id)

models.py

class Matriline(db.Model):
    __tablename__ = 'matriline'
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.Unicode(64))
    calls = db.relationship('Call', backref='matriline', lazy='select')
    pod_id = db.Column(db.Integer, db.ForeignKey('pod.id'))

    def __unicode__(self):
        return self.name

    def __str__(self):
        return self.name


class Pod(db.Model):
    __tablename__ = 'pod'
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.Unicode(64))
    matrilines = db.relationship('Matriline', backref='pod', lazy='select')
    clan_id = db.Column(db.Integer, db.ForeignKey('clan.id'))

    def __unicode__(self):
        return self.name
    def __str__(self):
        return self.name


class Clan(db.Model):
    __tablename__ = 'clan'
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.Unicode(64))
    pods = db.relationship('Pod', backref='clan', lazy='select')

    def __unicode__(self):
        return self.name

Answer 1

I solve this problem by process_data

def on_form_prefill(self, form, id):
    form.clan.choices = [(1, "first"), (2, "second")]
    form.clan.process_data(2)

I hope this can help you

Answer 2

I have a very similar problem and made it work by re-processing only the changed field. Also I needed to pass the currently set value in again (else it would be always set to the default):

from wtforms.utils import unset_value

class CustomView:
    def on_form_prefill(self, form, id):
        form.clan.choices = [(1, "first"),(2,"second")]
        form.clan.default = 2
        form.clan.process(None, form.clan.data or unset_value)

NOTE: As on_form_prefill is only called in the edit_view and not in the create_view this does only work with existing instances.