FormCollection self.instance bug due to FormCollection.full_clean()

[codematsing]

Given

#models.py
class ParentModel(self):
    name = models.CharField
    
class ChildModel(self):
    parent = models.ForeignKey(Parent, related_name='children', on_delete=models.CASCADE)
    name = models.CharField

#forms.py
class ChildForm(ModelForm):
  class Meta:
    model = ChildModel()
    fields = '__all__'

class ParentChildFormCollection(FormCollection):
    child_formset = ChildForm()

class UpdateView(SingleObjectMixin, FormCollectionView):
    model = ParentModel
    collection_class = ParentChildFormCollection()

    def get_initial():
      parent_object = self.get_object()
      initial = [
        {"child_form": {child.name for child in parent.children.all()}}
      ]
      return initial

Expectation:

#forms.py
class ParentChildFormCollection():
  def save(self):
    logger.info(self.instance.name)
    logger.info(type(self.instance))
    ...

• Expectation self.instance.name should consistently be the parent_object.name passed in FormCollectionView.get_form_kwargs()

Actual Results:

• self.instance.name would refer to the last object child.name after FormCollection.full_clean()

Observations:

# in class FormCollection
    def full_clean(self):
       ...
        logger.info(instance) #print parent_name
        if holder.is_valid():
            valid_holders[name] = holder
            logger.info(instance) #prints_child_name
      ...

Note:
I'll to replicate this in django-formset using the repo. I'll get back to you on this as I'm swamped at the moment.

[codematsing]

Replicated:
releases/1.5...codematsing:django-formset-debug:releases/1.5

How to test:

• Go to: http://127.0.0.1:8000/bootstrap/companydepartmentformset
• Check CompanyDepartmentUpdateView.form_kwargs. It replicates the functionality of UpdateViews passing a form_kwargs["instance"] to Form
• Expectation is that the first Company Instance in the database will be used but retained throughout the process since Company data is not changed in saving mechanism
• type more than one department name in form and submit. For my case, I added once department with name="new"
• Check console logs

Notes:
I did add my workaround so that form collection functionality will not interfere with self.instance data but I bet there's a better approach to this

Why is this important:

• I believe there are a lot of usecases where you would want to use a FormCollection on an UpdateView.
• Since native django uses ModelForm.instance to pass UpdateView.object to form, UpdateView.object data would be accidentally changed due to integration of FormCollectionView

How I stumbled upon this issue

• My saving implementation for a model with similar relationship as Company ||--o{ Department would go as follow

class CompanyDepartmentUpdateView(SingleObjectMixin, FormCollectionView):
     model = Company
     collection_class = CompanyDepartmentFormset

     def form_collection_valid(self, form_collection):
          form_collection.save()

class FormCollection(FormCollection):
     department_formset = DepartmentForm()

     def save(self):
         for department_kwargs in self.cleaned_data['department_formset']:
               Department.objects.create(company=self.instance, **deparment_kwargs)

[jrief]

Thanks for creating a runnable demo, appreciate that. I'll have a look at it.

[codematsing]

Sure thing! I really love using your library and happy to help on improving on it!