Django 'QuerySet' обект няма атрибут 'split' с помощта на modelform

Имам проблем с получаването на моя изглед за актуализиране на многотомани поле. Той връща това, след като формулярът бъде изпратен.

Traceback:
File "/usr/local/lib/python2.7/dist-packages/django/core/handlers/base.py" in get_response
  111.                         response = callback(request, *callback_args, **callback_kwargs)
File "/home/footbook/Ubuntu One/webapps/fb/poc/../poc/activity/views.py" in activity_save_page
  44.             group_names = form.cleaned_data['groups'].split()

Exception Type: AttributeError at /activity_save/
Exception Value: 'QuerySet' object has no attribute 'split'

Ето ги файловете. Models.py

class Group (models.Model):
    group_nm = models.CharField(max_length=64)
    group_desc = models.CharField(max_length=250)
    created = models.DateTimeField(auto_now_add=True)
    active_yn = models.BooleanField(default=True)
    def __unicode__(self):
        return self.group_nm



class Activity(models.Model):
    activity_nm = models.CharField(max_length=60)  
    activity_desc = models.CharField(max_length=250)
    startdt = models.DateField()
    enddt = models.DateField()
    crdt = models.DateTimeField(auto_now_add=True,editable=False)
    groups =  models.ManyToManyField(Group)
    upddt = models.DateTimeField(editable=False)
    def  save(self, *args, **kwargs):
        if not self.id:
            self.crdt = datetime.date.today()
        self.upddt = datetime.datetime.today()
        super(Activity, self).save(*args, **kwargs)
    def __unicode__(self):
        return self.name     

forms.py

def make_custom_datefield(f):
    formfield = f.formfield()
    if isinstance(f, models.DateField):
        formfield.widget.format = '%m/%d/%Y'
        formfield.widget.attrs.update({'class':'datePicker', 'readonly':'true'})
    return formfield


class ActivitySaveForm(forms.ModelForm):
    formfield_callback = make_custom_datefield
    def __init__(self, *args, **kwargs):
        super(ActivitySaveForm, self).__init__(*args, **kwargs)
        self.fields['activity_nm'].label = "Activity Name"
        self.fields['activity_desc'].label = "Describe It"
        self.fields['startdt'].label = "Start Date"
        self.fields['enddt'].label = "End Date"
        self.fields['groups'].label ="Group"
    class Meta:
        model = Activity

views.py

def activity_save_page(request):
    if request.method == 'POST':
        form = ActivitySaveForm(request.POST)
        if form.is_valid():
            act, created = Activity.objects.get_or_create(
                activity_nm = form.cleaned_data['activity_nm']
            )
            act.activity_desc = form.cleaned_data['activity_desc']
            if not created:
                act.group_set.clear()
            group_names = form.cleaned_data['groups'].split()
            for group_name in group_names:
                group, dummy = Group.objects.get_or_create(group_nm=group_name)
                act.group_set.add(group)
            act.save()
            return HttpResponseRedirect('/activity/')
    else:
        form = ActivitySaveForm()
    variables = RequestContext(request, {
        'form': form
    })
    return render_to_response('activity_save.html', variables)

Мисля, че щеше да работи, ако не използвах modelform, но имам нужда от него, за да внедря този инструмент за избор на дати. Тъй като полето е много-много, искам да ги разделя, когато бъдат въведени в базата данни, но моят набор от заявки е неуспешен. Опитах да променя това по куп различни начини, но останах. Виждал съм много подобни въпроси, но те или имаха външни ключове, или нямаха моделна форма.

Благодаря.

РЕДАКТИРАНЕ: activity_save.html

{% extends "base.html" %}
{% block title %}Save Activity{% endblock %}
{% block head %}Save Activty{% endblock %}
<input class="datePicker" readonly="true" type="text" id="id_startdt" />
<input class="datePicker" readonly="true" type="text" id="id_enddt" />
{% block content %}


<form action="{% url activity.views.activity_save_page act_id%}" method="post">{% csrf_token %}

{{ form.as_p }} 

<input type="submit" value="save it" />
</form>
{% endblock %}