Calling multiple instances at the same time for inline FormSets

Question

I'm having trouble displaying an inline formset with multiple instance objects. I want a list of all Owner and an inline formset of all their Pet, all one one page.

Code below works but calls 1 owner object at a time. Any suggestions?

This is a new question that came from: Django DatabaseError "more than one row returned by a subquery used as an expression" Editable related fields to object

models.py

class Teacher(models.Model):
    teacher = models.CharField(max_length=300)

class Owner(models.Model):
   relevantteacher = models.ForeignKey(Teacher)     
   owner = models.CharField(max_length=300)

class PetName(models.Model):
    relevantowner = models.ForeignKey(Owner)
    pet_name = models.CharField(max_length=50)

forms.py

class OwnerForm(forms.ModelForm):
    class Meta:
       model = Owner

PetNameFormSet = inlineformset_factory(Owner,
    PetName,
    can_delete=False,
    extra=3,
    form=OwnerForm)

views.py

def petname(request, teacher_id):
   teacher = get_object_or_404(Teacher, pk=teacher_id)

   owners = Owner.objects.filter(relevantteacher=teacher_id)
   owner = owners[0]

   if request.method == "POST":
      petNameInlineFormSet = PetNameFormSet(request.POST, request.FILES, instance=owner)

      if petNameInlineFormSet.is_valid():
         petNameInlineFormSet.save()

         return HttpResponseRedirect(reverse('success'))

   else:
      petNameInlineFormSet = PetNameFormSet(instance=owner) 

   context = {'teacher': teacher, 'owner': owner, 'petNameInlineFormSet' : petNameInlineFormSet}
   return render(request, 'petname.html', context)

HTML petname.html

   {% load url from future %}
 <form class="petname_form" action="{% url "petname" teacher.id %}" method="post">{% csrf_token %}
   {{ teacher }}
   {{ owner.as_table }}
   {{ petNameInlineFormSet.as_table }}
 </form>

Update

HTML

{% for owner_form in owner_forms %}
    <form class="petname_form" action="{% url "petname" teacher.id %}" method="post">{% csrf_token %
     {% for o in owners %}
      {{o.owner}} has pets:<br/> //owner is the PK of the Owner model
         {{ owner_forms.relevantteacher }}
         {{ owner_forms.as_table }}
         {{ owner_forms.inline_form.as_table }}
     {% endfor %}
    </form>

Answer 1

Basically, what you need to do is compile a list of owner forms to render. Upon validating, you must preserve errors and success messages for each form, and render the result.

Here is a semi-pseudocode example based on your views.py for achieving the aforementioned:

owner_forms = []

if request.method == "POST":
    for owner in owners:
        #passing instance here may yeild unexpected behavior; django is aware of instance based on request.POST data.
        owner_form = PetNameFormSet(request.POST, request.FILES) 
        owner_forms.append(owner_form)

        if petNameInlineFormSet.is_valid():
            petNameInlineFormSet.save()

else:
    for owner in owners:
        owner_form = PetNameFormSet(instance=owner)
        owner_forms.append(owner_form)

context['owner_forms'] = owner_forms

Now, render each form in owner_forms:

{% for owner_form in owner_forms %}
    <form class="petname_form" action="{% url "petname" teacher.id %}" method="post">{% csrf_token %}
       {% refer to the teacher object associated with the object the form is generated on %}
       {{ owner_form.relevantteacher }}
       {{ owner_form.as_table }}
       {{ owner_form.inline_form.as_table }}
    </form>
{% endfor %}

Other recommendations:

1. max_length=300 is problematic depending on database being used. General rule of thumb is to limit CharField to 255 characters. Anything larger than 255 should be a TextField.
2. Django allows for referring to ForeignKeys lazily, replace instances of models.ForeignKey(Model) with models.ForeignKey("Model") to prevent potential race conditions in the future.