title: how to set default value for formset django
body: <p>i'm trying to build an app which contains django inline formset , but default values only show for the first form!?
  this is my model</p>
  <pre><code>class Main(models.Model):
       admin = models.ForeignKey(User,on_delete=models.CASCADE)
       A= models.ManyToManyField(Item,through='Child')
       B = models.IntegerField()
  
  class Child(models.Model):
       main = models.ForeignKey(Main,on_delete=models.CASCADE)
       item = models.ForeignKey(Item,on_delete=models.CASCADE)
       quantity = models.IntegerField(default=1)
  </code></pre>
  <p>my views.py</p>
  <pre><code>class CreateMainInlineFormset(LoginRequiredMixin,SuccessMessageMixin,CreateView):
      model = Main
      form_class = MainForm
      template_name = 'main/create.html'
      def get_context_data(self, *args,**kwargs):
          data = super().get_context_data(*args,**kwargs)
          if self.request.POST:
              data['items'] = ChildInlineFormSet(self.request.POST)
              data['items'].full_clean()
          else:
              data['items'] = ChildInlineFormSet()
          return data
  
      def form_valid(self, form):
          context = self.get_context_data()
          items = context['items']
  
          with transaction.atomic():
              self.object = form.save(commit=False)
              form.instance.admin = self.request.user
              if items.is_valid() and form.is_valid() and items.cleaned_data!={}:
                  items.instance = self.object
                  form.save(commit=True)
                  items.save()
              else:
                  return render(self.request,self.template_name,context)
      
          return super().form_valid(form)
      def get_success_url(self):
          return reverse_lazy('maininfo:list-item')
  </code></pre>
  <p>my forms.py</p>
  <pre><code>class ParentForm(forms.ModelForm):
  
      class Meta:
         model = Main
         fields = [
             '__all__'
         ]
  
  class ChildForm(forms.ModelForm):
  
      class Meta:
         model = Child
         fields = [
             '__all__'
         ]
  
   ChildInlineFormSet= inlineformset_factory(
      Main,Child,form=ChildForm,fields=(
         'item','quantity'),
         extra=1
      )
  </code></pre>
  <p>i have to display <code>quantity</code> default value for all of the forms , but it only display for the first form , the rest will be null</p>