Default the value of an external key in a form - django

Question

In the form for adding a calendar (of the Model "Calendar"), in the "group" field shows a drop-down menu where all the "CalendarGroups" are. I would like this menu not to be there and "group" to be set by default with the "group" id which I pass through the url parameter ("group_id"). How could I solve this?
In models.py:
class CalendarGroups(models.Model):
name = models.CharField(max_length = 155, blank=True, null=True, unique=True)
def __str__(self):
return str(self.name)
#property
def get_html_url(self):
url = reverse('', args=(self.id,))
return f' {self.name} '
class Calendar(models.Model):
name = models.CharField(max_length=200, unique=True)
#created_by
group = models.ForeignKey(CalendarGroups, on_delete = models.CASCADE, default='')
#property
def get_html_url(self):
url = reverse('cal:calendar_view', args=(self.id, self.group))
return f' {self.name} '
In forms.py:
class CalendarGroupsForm(ModelForm):
class Meta:
model = CalendarGroups
fields = ('name',)
def __init__(self, *args, **kwargs):
super(CalendarGroupsForm, self).__init__(*args, **kwargs)
class CalendarForm(ModelForm):
class Meta:
model = Calendar
fields = ('name', 'group')
def __init__(self, *args, **kwargs):
super(CalendarForm, self).__init__(*args, **kwargs)
In views.py:
def group(request, group_id=None):
instance = CalendarGroups()
if group_id:
instance = get_object_or_404(CalendarGroups, pk=group_id)
else:
instance = CalendarGroups()
form = CalendarGroupsForm(request.POST or None, instance=instance)
if request.POST and form.is_valid():
form.save()
return HttpResponseRedirect(reverse('cal:home'))
return render(request, 'cal/form.html', {'form': form})
def calendar(request, group_id=None):
instance = Calendar()
form = CalendarForm(request.POST or None, instance=instance)
if request.POST and form.is_valid():
form.save()
return HttpResponseRedirect(reverse('cal:home'))
return render(request, 'cal/form.html', {'form': form})
In urls.py:
url(r'^home/(?P<group_id>\d+)/calendar/new/$', views.calendar, name='calendar_new')

Answer 1

After consulting the documentation, I solved it by modifying the code as follows:
In views.py:
def calendar(request, group_id=None):
instance = Calendar()
instance = Calendar(group_id=group_id)
form = CalendarForm(request.POST or None, instance=instance)
if request.POST and form.is_valid():
form.save()
return HttpResponseRedirect(reverse('cal:home'))
return render(request, 'cal/form.html', {'form': form})
In forms.py:
class CalendarForm(ModelForm):
class Meta:
model = Calendar
fields = ('name',)
def __init__(self, *args, **kwargs):
super(CalendarForm, self).__init__(*args, **kwargs)

Answer 2

You already have send to the views.calendar the group_id key you need.
Now try to add it to the form before the form.save
Try to modify like this in view.py
def calendar(request, group_id):
instance = Calendar()
form = CalendarForm(request.POST or None, instance=instance)
if request.POST and form.is_valid():
form.group=group_id
form.save()
return HttpResponseRedirect(reverse('cal:home'))
return render(request, 'cal/form.html', {'form': form})
Take note that might override what user can post on CalendarForm and you should consider to hide or make not editable that filed group_id,
Also this is slightly different to what i usually do but it should work
I Post also an example of what works for me:
def calendar(request, group_id):
instance = Calendar()
form = CalendarForm(request.POST or None)
if request.POST and form.is_valid():
instance = form.save(commit=False)
instance.group = group_id
instance.save()
return HttpResponseRedirect(reverse('cal:home'))
return render(request, 'cal/form.html', {'form': form})