ModelForm “instance” parameter and foreign key field

Question

I'm trying to initialize an object with in "instance" parameter but it doesn't go into the form. It is a required one so is_valid fails. Can someone please advise, I'm almost sure it's an easy mistake but can't spot it.

FORM:

from django.forms import ModelForm

from tagging.forms import TagField

class BusinessEditForm(ModelForm):
tags = TagField()

class Meta:
    model = Business
    exclude = ('owner', 'pub_date')

Logic in views.py

if businessid:
    b = Business.objects.get(id=businessid)
    category = b.category
    assert(b.owner == request.user) or request.user.is_staff
    #form = forms.BusinessEditForm(request.POST, instance=b)
else:
    assert category.is_public or request.user.is_staff
    b = Business(owner=request.user, category_id=category.id)
    # form = forms.BusinessEditForm(request.POST, instance=b)
    isNew = True

if request.method == "POST":
    form = forms.BusinessEditForm(request.POST, instance=b)

    if form.is_valid():

This last line validates to False.

Any help is welcome.

Thanks, Igor

Answer 1

If you need to pass instance to the form as if it was part of the form data, maybe you can try something like this:

if request.method == "POST":
    form_data = request.POST.copy()
    form_data['instance'] = b
    form = forms.BusinessEditForm(form_data)

Answer 2

If you're excluding required fields in the form, you'll need to set them programatically before calling is_valid() because the form wouldn't create a valid Business object otherwise. This is why is_valid() is returning False .

Answer 3

Without cluttering your views you could write into your forms clean method:

def clean(self):
  self.cleaned_data.update(excluded_field=self.instance.excluded_field)
  return super(YourForm, self).clean()

But you then should also require in your forms __init__ method, that the instance is given and has your excluded fields set.