Django Multiple Choice Field / Checkbox Select Multiple

Question

I have a Django application and want to display multiple choice checkboxes in a user's profile. They will then be able to select multiple items.

This is a simplified version of my models.py:

from profiles.choices import SAMPLE_CHOICES

class Profile(models.Model):
    user = models.ForeignKey(User, unique=True, verbose_name_('user'))
    choice_field = models.CharField(_('Some choices...'), choices=SAMPLE_CHOICES, max_length=50)

And my form class:

class ProfileForm(forms.ModelForm):
    choice_field = forms.MultipleChoiceField(choices=SAMPLE_CHOICES, widget=forms.CheckboxSelectMultiple)

    class Meta:
        model = Profile

And my views.py:

if request.method == "POST":
    profile_form = form_class(request.POST, instance=profile)
    if profile_form.is_valid():
        ...
        profile.save()
return render_to_response(template_name, {"profile_form": profile_form,}, context_instance=RequestContext(request))

I can see that the POST is only sending one value:

choice_field u'choice_three' 

And the local vars params is sending a list:

[u'choice_one', u'choice_two', u'choice_three']

All of the form fields display correct, but when I submit a POST, I get an error

`Error binding parameter 7 - probably unsupported type.`  

Do I need to process the multiple choice field further in the view? Is the model field type correct? Any help or references would be greatly appreciated.

Answer 1

The profile choices need to be setup as a ManyToManyField for this to work correctly.

So... your model should be like this:

class Choices(models.Model):
  description = models.CharField(max_length=300)

class Profile(models.Model):
  user = models.ForeignKey(User, blank=True, unique=True, verbose_name_('user'))
  the_choices = models.ManyToManyField(TheChoice)

Then, sync the database and load up Choices with the various options you want available.

Now, the ModelForm will build itself...

class ProfileForm(forms.ModelForm):
  Meta:
    model = Profile
    exclude ['user']

And finally, the view:

if request.method=='POST':
  form = ProfileForm(request.POST)
  if form.is_valid():
    profile = form.save(commit=False)
    profile.user = request.user
    profile.save()
else:
  form = ProfileForm()

return render_to_response(template_name, {"profile_form": form}, context_instance=RequestContext(request))

It should be mentioned that you could setup a profile in a couple different ways, including inheritance. That said, this should work for you as well.

Good luck.

Answer 2

Brant's solution is absolutely correct, but I needed to modify it to make it work with multiple select checkboxes and commit=false. Here is my solution:

models.py

class Choices(models.Model):
    description = models.CharField(max_length=300)

class Profile(models.Model):
   user = models.ForeignKey(User, blank=True, unique=True, verbose_name_('user'))
   the_choices = models.ManyToManyField(Choices)

forms.py

class ProfileForm(forms.ModelForm):
    the_choices = forms.ModelMultipleChoiceField(queryset=Choices.objects.all(), required=False, widget=forms.CheckboxSelectMultiple)

class Meta:
    model = Profile
    exclude = ['user']

views.py

if request.method=='POST':
    form = ProfileForm(request.POST)
    if form.is_valid():
        profile = form.save(commit=False)
        profile.user = request.user
        profile.save()
        profile.save_m2m() # needed since using commit=False
    else:
        form = ProfileForm()

return render_to_response(template_name, {"profile_form": form}, context_instance=RequestContext(request))

Answer 3

The models.CharField is a CharField representation of one of the choices. What you want is a set of choices. This doesn't seem to be implemented in django (yet).

You could use a many to many field for it, but that has the disadvantage that the choices have to be put in a database. If you want to use hard coded choices, this is probably not what you want.

There is a django snippet at http://djangosnippets.org/snippets/1200/ that does seem to solve your problem, by implementing a ModelField MultipleChoiceField.