In Django, Effectively Allowing Addition and Removal of Related Models

I’m very new with Django and am happy to accept criticism or suggestions on better ways to do this.

The use case for what I’ve done is this: I’m working on a database to track membership for a small political committee. One of the things we’re interested in is the districts in which our members live. There are different types of districts that we want to track including voting precincts, municipal boroughs, state house districts, state senate districts, and U.S. congressional districts.

For creating or editing a person’s information, there should be a single select box for each type of district. But I want admins to be able to add and remove district types through the admin panel.

To make this work, I have four models: Person, District, DistrictType, and Residency. Residency is an intermediate model for Person and District, but I defined it as a class instead of letting Django create it.

Here is a very simplified version of my models:
Models.py

class DistrictType(models.Model):
    name = models.CharField('Name', max_length=30, help_text='The name of the type of district')

    def __str__(self):
        return self.name


class District(models.Model):
    name = models.CharField('Name', max_length=30, help_text='The name of the type of district')
    district_type = models.ForeignKey(DistrictType, on_delete=models.SET_NULL, null=True)

    def __str__(self):
        return self.name

class Person(models.Model):
    name=models.CharField('Name', max_length=30, help_text='The person's full name'

    def__str__(self):
        Return self.name

class Residency(models.Model):
    district = models.ForeignKey(District, on_delete=models.CASCADE, help_text='The district in which the person lives')
    person = models.ForeignKey(Person, on_delete=models.CASCADE, help_text='The person who lives in the district')

    def __str__(self):
        return self.district + ': ' + self.person

 

I want admin to be able to add and remove districts and district types.

admin.py

from .models import District, DistrictType

class DistrictAdmin(admin.ModelAdmin):
    list_display = ( "name", "district_type")
admin.site.register(District, DistrictAdmin)

class DistrictTypeAdmin(admin.ModelAdmin):
    list_display = ( "name")
admin.site.register(DistrictType, DistrictTypeAdmin)

 

With District and DistricType registered, admins can add and remove district types (and districts) as needed.

I want users to be able to add and edit people without using the admin panel, and I want the person form to have one select box for each type of district. Of course, I have permissions set to restrict who can add and edit people, but I’m not covering that here.

If, for example, I have four types of districts, I want four select boxes on the person form. Each of those select boxes represents a residency. So I have to define a residency form to be used as an inline model form.

forms.py

class PersonForm(ModelForm):
    class Meta:
        model = Person
        fields = (
            "name",
        )

class ResidencyForm(ModelForm):
    district_type_name = forms.CharField(required=False)
    class Meta:
        model = Residency
        fields = (
            "district",
        )

 

Note that district_type_name is not part of the residency model and won’t be used in the update or creation of the object. The reason it is there will be explained below.

The residency model has two fields, person and district, but only district is needed here because person will be taken care of by the formset factory.

views.py

class PersonCreate(CreateView):
    model = Person
    form_class=PersonForm

    district_type_all = DistrictType.objects.all()
    district_type_count = DistrictType.objects.count()

    ResidencyFormSet = inlineformset_factory(Person, Residency, form=ResidencyForm, extra=district_type_count, max_num=district_type_count, fields='__all__')

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

        residencies = self.ResidencyFormSet( instance = self.object )
        for i in range( self.district_type_count):
            residencies.forms[i].fields['district'].queryset = District.objects.filter(district_type__id=self.district_type_all[i].id)
            residencies.forms[i].fields['district_type_name'].initial = self.district_type_all[i].name
            context['district_label_' + str(i)] = self.district_type_all[i].name
        context['residencies'] = residencies

        return context

    def form_valid(self, form):

        self.object = form.save()

        context = self.get_context_data()

        residencies = context['residencies']
        if residencies.is_valid():
            residencies.save()

        return super(PersonCreate, self).form_valid(form)

 

If you don’t understand inline formsets, I think Daniel Chen’s post will explain their use a lot better than the Django docs.

With the line

ResidencyFormSet = inlineformset_factory(Person, Residency, form=ResidencyForm, extra=district_type_count, max_num=district_type_count, fields='all')

, I created a set of inline forms. The first parameter, Person, defines the parent model. This is why I don’t need a person field in my form definition. The extra parameter defines how many inline forms to display. I want that number to match the amount of district types.

The max_num parameter ensures there will be no more forms displayed than the amount of district types. It’s not necessary in the creation view, although I included it here, but it is necessary in the update view. Without it, there would be four extra select boxes in addition to those that already have data from the previous update or creation.

At this point, I would have four identical inline forms, each with a select box that includes every district in the database. But I want to limit each select box to a certain district type. This is where I think I’m breaking new ground.

Here’s another look at get_context_data in views.py

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

        residencies = self.ResidencyFormSet( instance = self.object )
        for i in range( self.district_type_count):
            residencies.forms[i].fields['district'].queryset = District.objects.filter(district_type__id=self.district_type_all[i].id)
            residencies.forms[i].fields['district_type_name'].initial = self.district_type_all[i].name
        context['residencies'] = residencies

        return context

 

In get_context_data, I go through each of the residency forms in the formset, and update the queryset for it’s select box. Now each select box is limited to districts of a certain district type.

Here’s where that extra district_type_name field comes in. The default label for the district field is “District”. But on the form, I want each label to be the name of the district type that the select box is limited to. So I populate the unbound field district_type_name with the name of the district type, and use that value as the label.

From person_form.html in my templates directory


    {% csrf_token %}
    <div class="section" >
        Name
        <div class="row" >
            <div class="label" >
                Full Name
            </div >
            <div class="fields" >
                <div class="field" >
                    {{ form.given_name }}
                </div >
            </div >
        </div >
    </div >

    {{ residencies.management_form }}
    <div class="section" >
        Districts
        {% for form in residencies.forms %}
            <div class="row" >
                <div class="label" >
                    {{ form.district_type_name.value }}
                </div >
                <div class="fields" >
                    <div class="field" >
                        {{ form.district }}
                    </div >
                </div >
            </div >
        {% endfor %}
    </div >

    

Here I used district_type_name.value as the label for each select box

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