filter-by support on form collections?

[codematsing]

Hi Jacob!

It's been a long time! I've checked on the items I've mentioned before when we met and it looks like they've been resolved after I've updated the version I've been using. The only thing I haven't done is to check on django-filer.

On another note, I'd like to ask if you think there's some flexibility to support filter by on fomcollections? I have a particular use case in need of this but I also think that it is a general usecase to consider.

For example, in reference to the State and County relationship. Someone may have a usecase to create a company directory where a companies are restricted to operate on particular states only. Consequently, they may open multiple branches on different counties. Here, we might want to construct a FormCollection such as:

# models
class Company(models.Model):
    name = models.CharField()
    state = models.ForeignKey(State)

class Branch(models.Model):
   county = models.ForeignKey(County)
   contact_information = models.CharField()

# forms
class CompanyForm(ModelForm):
    class Meta:
        fields = ['name', 'state']

class BranchForm(ModelForm):
    county = forms.ModelChoiceField(
        widget = Selectize(
              # the objective of the support in form collection
              # is to ensure valid entries of counties in formset
              # based on encoded state on the parent form
              # something like...
              filter_by={'company_form.state':'state__id'}
        )
    )

    class Meta:
        fields = ['contact_information', 'county']
    
class BranchFormset(FormCollection):
    legend = "Branches"
    branch_form = BranchForm()
    min_siblings=1

class CompanyLocationForm(FormCollection):
    company_form = CompanyForm()
    branch_formset = BranchFormset()

Processing the code:

I've been reading through the following references for the use of filter-by:

• IncompleteResponseMixin
• IncompleteSelect.loadOptions and IncompleteSelect.buildFetchQuery

I followed that for the backend (py) code:

class IncompleteSelectResponseMixin:
    def get(self, request, **kwargs):
        # incharge of reloading form field options
        if request.accepts('application/json') and 'field' in request.GET:
            return self._fetch_options(request)
        return super().get(request, **kwargs)

I followed also that for the frontend (ts) code:

• IncompleteSelect.setupFilters
• references to reloadOptions, loadOptions and buildFetchQuery

I'm still trying to digest the code fully but I wonder if you see a way to create an even listener for onChange of field company_form.state, and to trigger buildFetchQuery that would look something like:
<url>?offset=0&filter-state=##&field=branch_formset.0.branch?

or would this be complicating things and you see a different approach to filtering options within a formset based on another form?

I also wonder if the use of django_filter's FilterSet could resolve this issue but I'm still studying the implementation for this as I think there is a gap in the documentation that does not fully explain how the state: forms.ModelChoiceField value is passed to the StateFilterSet.qs