ModelForm is_valid() accepts options outside choices

[hayrynen@…]

If form is made using ModelForm and choices of ManyToMany field are limited like this:

# models.py

class Product(models.Model):
   name = models.CharField(max_length=60, verbose_name="Name")
   visibility = models.ManyToManyField(Group, verbose_name="Groups")

# views.py

class ProductForm(forms.ModelForm):
   def __init__(self, group_choices, *args, **kwargs):
       super(ProductForm, self).__init__(*args, **kwargs)
       self.fields['visibility'].choices = group_choices
   class Meta:
       model = Product

@login_required
def products_view(request):
   userprofile = UserProfile.objects.get(user = request.user)
   groups = [ (i.id, i.group) for i in Membership.objects.filter(userprofile=userprofile) ]

   if request.method == "POST":
       form = ProductForm(groups, request.POST)
       if form.is_valid():
           .. do stuff with visibility trusting form.is_valid()

is_valid() allows values for ManyToMany selections outside what is specified in the form as long as there exists corresponding ID in the database. Obviously the submitted form needs to be modified outside standard browser UI.

is_valid() should compare selections against .choices, not against what exists in the database.

[Aymeric Augustin]

Fixed formatting -- please use wiki syntax and preview.

[Dan Poirier]

From ​https://docs.djangoproject.com/en/dev/topics/forms/modelforms/:

  ManyToManyField is represented by django.forms.ModelMultipleChoiceField, which is a MultipleChoiceField whose choices are a model QuerySet.

Validation of a ModelMultipleChoiceField is controlled by the queryset value, not choices.

[Simon Charette]

@hayrynen I think you should try using queryset attribute instead.

class ProductForm(forms.ModelForm):
   def __init__(self, visibility_qs, *args, **kwargs):
       super(ProductForm, self).__init__(*args, **kwargs)
       self.fields['visibility'].queryset = visibility_qs
   class Meta:
       model = Product

@login_required
def products_view(request):
   userprofile = UserProfile.objects.get(user = request.user)
   # assuming Membership.group's related_name is unset
   visibility_qs = Groups.objects.filter(membership_set__userprofile=userprofile)

   if request.method == "POST":
       form = ProductForm(visibility_qs, request.POST)
       if form.is_valid():
           .. do stuff with visibility trusting form.is_valid()