Question about m2m and forms

[Carlo Ascani]

Hi all,

I have a model A with a m2m to B:

------------------------------------------
class A(models.Model):
to_b = models.ManyToManyField(B)

class B(models.Model):
name = models.CharField(max_length=100)
------------------------------------------


In a view, I am listing A objects and I am building
a form to use B as a filter.


------------------------------------------
class AFilterForm(forms.Form):
to_b = forms.ModelMultipleChoiceField(
widget=forms.CheckboxSelectMultiple(),
queryset = B.objects.all())
------------------------------------------


This is the view:


------------------------------------------
class AListViewWithFilter(ListView):
model = A

def get_context_data(self, **kwargs):
context = super(AListViewWithFilter, self).get_context_data(**kwargs)

qs = A.objects.all()
b_filter = None
if self.request.GET:
if 'to_b' in self.request.GET:
b_filter = self.request.GET.getlist('to_b')
res = res.filter(to_b__in=b_filter).distinct()

context.update({
'results': qs,
'form': AFilterForm(initial={
'to_b': b_filter
})
return context
------------------------------------------


Everything is working fine.

I would like to add a count of how many A objects are there
for any of the to_b. So that the filter form would look like this:

[ ] to_b_value_1 (34)
[ ] to_b_value_2 (12)
[ ] to_b_value_3 (3)
...

Is that possible?

Thank you in advance

Best,
Carlo


--
Carlo Ascani aka carloratm
Frontend Developer

www.carlorat.me
carloratm@freenode

[Matthew Pava]

Hi Carlos,
You probably want to create a new widget and override its label_from_instance method.

class BModelMultipleChoiceField(forms.ModelMultipleChoiceField):
def label_from_instance(self, obj):
return "%s (%s)" % (obj, obj.count_a)


And then you'll want to change your queryset to annotate the count so you can access it in the new field.
class AFilterForm(forms.Form):
to_b = BModelMultipleChoiceField(
widget=forms.CheckboxSelectMultiple(),
queryset = B.objects.all().annotate(count_a=Count('a_set')))

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[Carlo Ascani]

Il giorno venerdì 17 febbraio 2017 20:09:15 UTC+1, Matthew Pava ha scritto:

Hi Carlos,
You probably want to create a new widget and override its label_from_instance method.

class BModelMultipleChoiceField(forms.ModelMultipleChoiceField):
        def label_from_instance(self, obj):
                return "%s (%s)" % (obj, obj.count_a)


And then you'll want to change your queryset to annotate the count so you can access it in the new field.
class AFilterForm(forms.Form):
        to_b = BModelMultipleChoiceField(
                widget=forms.CheckboxSelectMultiple(),
                queryset = B.objects.all().annotate(count_a=Count('a_set')))

 Thank you!

That works really well.

[Carlo Ascani]

The next step to this is would be to put the count in a separate property, so I can render it independently in the template (in a span, for example)

is that possible ?

Thank you in advance

Carlo