ModelMultipleChoiceField forcing required

[Scot Hacker]

I'm having a strange issue with a pair of ManyToManyFields, where they're acting like they're required fields in the admin even though they're not.

# In models.py

    instructors = models.ManyToManyField(Instructor, blank=True)
    students = models.ManyToManyField(Profile, blank=True)

I can update an instance of this model with no instructors or students from the CLI just fine. The fields are not required. But I'm using ModelMultipleChoiceField in the admin:

# In admin.py

class OfferingAdminForm(forms.ModelForm):

    instructors = forms.ModelMultipleChoiceField(
        widget = widgets.FilteredSelectMultiple('Instructors',is_stacked=False),
        queryset = Instructor.objects.all())


    students = forms.ModelMultipleChoiceField(
        widget = widgets.FilteredSelectMultiple('Students',is_stacked=False),
        queryset = User.objects.filter(is_active=True))

and when I try to save via the admin, it tells me these fields are required. If I tweak it to not use this ModelForm, I can save without instructors or students just fine. 

Theories? Thanks.

[Carl Meyer]

Hi Scot,

When you override a field in a ModelForm, you lose the ability for it to
automatically pick up configuration from the model field. Either the
field is auto-created by the ModelForm based on your model field, or it
is created manually by you; it can't be both.

So because you are manually creating your `instructors` and `students`
fields on the form, the `blank=True` in the model has no effect; you
need to pass `required=False` to your two form fields.

(Because of this, I frequently choose to update/tweak form fields in an
overridden `__init__` method of a ModelForm, rather than overriding the
fields entirely.)

Carl

[Scot Hacker]

On Wednesday, November 5, 2014 11:15:47 AM UTC-8, Carl Meyer wrote:

So because you are manually creating your `instructors` and `students`
fields on the form, the `blank=True` in the model has no effect; you
need to pass `required=False` to your two form fields.

Got it, right you are - that works fine. 

 

(Because of this, I frequently choose to update/tweak form fields in an
overridden `__init__` method of a ModelForm, rather than overriding the
fields entirely.)

Makes sense! 

Thanks,

./s