How to Implement 3-way Dependent/Chained Dropdown List with Django?

Question

I am using django and postgresql. I'm dealing with a 3-way dependent drop-down list. After adding the country selection, the province area is automatically updated depending on the selected country. After selecting a province, the county field opens only when the page is refreshed. I would be glad if you help me in this regard.

models.py

from django.db import models

class Country(models.Model):
    name = models.CharField(max_length=30)

    def __str__(self):
        return self.name

class City(models.Model):
    country = models.ForeignKey(Country, on_delete=models.CASCADE)
    name = models.CharField(max_length=30)

    def __str__(self):
        return self.name

class District(models.Model):
    city = models.ForeignKey(City, on_delete=models.CASCADE)
    name = models.CharField(max_length=30)

    def __str__(self):
        return self.name

class Person(models.Model):
    name = models.CharField(max_length=100)
    birthdate = models.DateField(null=True, blank=True)
    country = models.ForeignKey(Country, on_delete=models.SET_NULL, null=True)
    city = models.ForeignKey(City, on_delete=models.SET_NULL, null=True)
    district = models.ForeignKey(District, on_delete=models.SET_NULL, null=True)

    def __str__(self):
        return self.name

forms.py

from django import forms
from .models import Person, Country, City, District

class PersonForm(forms.ModelForm):
    class Meta:
        model = Person
        fields = ('name', 'birthdate', 'country', 'city', 'district')

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.fields['city'].queryset = City.objects.none()

        if 'country' in self.data:
            try:
                country_id = int(self.data.get('country'))
                self.fields['city'].queryset = City.objects.filter(country_id=country_id).order_by('name')
            except (ValueError, TypeError):
                pass  # invalid input from the client; ignore and fallback to empty City queryset
        elif self.instance.pk:
            self.fields['city'].queryset = self.instance.country.city_set.order_by('name')

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.fields['district'].queryset = District.objects.none()

        if 'city' in self.data:
            try:
                city_id = int(self.data.get('city'))
                self.fields['district'].queryset = District.objects.filter(city_id=city_id).order_by('name')
            except (ValueError, TypeError):
                pass  # invalid input from the client; ignore and fallback to empty District queryset
        elif self.instance.pk:
            self.fields['district'].queryset = self.instance.city.district_set.order_by('name')

views.py

def load_cities(request):
    country_id = request.GET.get('country')
    cities = City.objects.filter(country_id=country_id).order_by('name')
    return render(request, 'neighbor/city_dropdown_list_options.html', {'cities': cities})

def load_districts(request):
    city_id = request.GET.get('city')
    districts = District.objects.filter(city_id=city_id).order_by('name')
    return render(request, 'neighbor/district_dropdown_list_options.html', {'districts': districts})

templates.html

<h2>Person Form</h2>
  <form method="post" id="personForm" data-cities-url="{% url 'ajax_load_cities' %}" novalidate>
    {% csrf_token %}
    <table>
      {{ form.as_table }}
    </table>
    <button type="submit">Save</button>
    <a href="{% url 'person_changelist' %}">Nevermind</a>
  </form>
  <script src="https://code.jquery.com/jquery-3.3.1.min.js"></script>
  <script>
    $("#id_country").change(function () {
      var url = $("#personForm").attr("data-cities-url");
      var countryId = $(this).val();
      $.ajax({
        url: url,
        data: {
          'country': countryId
        },
        success: function (data) {
          $("#id_city").html(data);
        }
      });
    });
    $("#id_city").change(function () {
      var url = $("#personForm").attr("data-districts-url");
      var cityId = $(this).val();
      $.ajax({
        url: url,
        data: {
          'city': cityId
        },
        success: function (data) {
          $("#id_district").html(data);
        }
      });
    });
  </script>

I'm referring to the example here.

https://simpleisbetterthancomplex.com/tutorial/2018/01/29/how-to-implement-dependent-or-chained-dropdown-list-with-django.html

Answer 1

1. In your templates.html file, you are calling the same URL hence the same view for country and city fields change. you need to make a new URL to handle the request in load_district view.
   
   make the following changes

   $("#id_city").change(function () { var url = $("#personForm").attr("data-districts-url"); var cityId = $(this).val(); $.ajax({ url: '{% url 'ajax_load_districts' %}', data: { 'city': cityId }, success: function (data) { $("#id_district").html(data); } }); });

2. you don't need to modify init() method twice, just remove these 2 lines from froms.py. (line number 22 and 23)

    def __init__(self, *args, **kwargs): super().__init__(*args, **kwargs)

3. add a new URL for handling ajax request for district

   path('ajax/load-district/', views.load_districts, name='ajax_load_districts'),

you can clone this example, i have used Country, City, Vanue... https://github.com/masbhanoman/django_3way_chained_dropdown_list

Answer 2

Thank you very much for your answer and the link to GitHub. It works perfectly with 3 dependent dropdown lists. You can still slightly improve your JS code:

var url = $("#personForm").attr("data-districts-url");

can be deleted as you don't use the variable and directly set an url, which, by the way, makes your code quite readable.

Answer 3

One addition point here is regarding the id formatting, so in my case was necessary to use {{ value|safe }} on dropdown, so:

<option value="">---------</option>
{% for city in cities %}
<option value="{{ city.pk|safe }}">{{ city.name }}</option>
{% endfor %}