How can I filter by related model fields and support multiple selections using django-filter?

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Hello,

I am using the django-filter extension to filter records in my queryset. So far, I have only filtered fields from a single model, but now I want to include filtering based on data from a related model via an FK—in this case, filtering by the traffic_light field from the Status model. Additionally, I need to filter by multiple values rather than a single record.

Here are the two models involved:

PYTHON
class Responsibility(models.Model):
    project = models.ForeignKey(Project, on_delete=models.CASCADE, verbose_name='Projekt')
    system = models.ForeignKey(System, on_delete=models.CASCADE, verbose_name='Baugruppe')
    team = models.ForeignKey(Team, on_delete=models.CASCADE, verbose_name='Team')
    employee = models.ForeignKey(Employee, on_delete=models.SET_NULL, blank=True, null=True, verbose_name='Mitarbeiter')
    created_at = models.DateTimeField(auto_now_add=True, editable=False, blank=True, verbose_name='Erstelldatum')
    updated_at = models.DateTimeField(auto_now=True, editable=False, blank=True, verbose_name='Änderungsdatum')

    class Meta:
        verbose_name = 'Verantwortlichkeit'
        verbose_name_plural = 'Verantwortlichkeiten'
        constraints = [
            models.UniqueConstraint(fields=['project', 'system', 'team', 'employee'], name='uq_project_system_team_employee')
        ]

    def __str__(self):
        return f'{self.project} | {self.system} | {self.team} | {self.employee}'

class Status(models.Model):
    COLORS = (
        ('Rot', 'Rot'),
        ('Gelb', 'Gelb'),
        ('Grün', 'Grün'),
    )   
    responsibility = models.OneToOneField(Responsibility, on_delete=models.CASCADE, unique=True, verbose_name='Verantwortlichkeit')
    traffic_light = models.CharField(max_length=4, choices=COLORS, default='Grün', verbose_name='Ampel')
    created_at = models.DateTimeField(auto_now_add=True, editable=False, blank=True, verbose_name='Erstelldatum')
    updated_at = models.DateTimeField(auto_now=True, editable=False, blank=True, verbose_name='Änderungsdatum')

    class Meta:
        verbose_name = 'Status'
        verbose_name_plural = 'Status'

    def __str__(self):
        return f'{self.responsibility} | {self.traffic_light}'

My current filters.py implementation is as follows:

PYTHON
import django_filters
from .models import Responsibility

class ResponsibilityFilter(django_filters.FilterSet):
    class Meta:
        model = Responsibility
        fields = ['project', 'system', 'team', 'employee']

I plan to extend this to include the traffic_light field from the Status model and enable filtering with multiple values. Below is the template code used for filtering:

HTML
        <div class="card-body bg-light">
            <form method="GET">
                <div class="row">
                    {% for field in responsibilities_filter.form %}
                        <div class="col fw-bold">
                            {{ field.label_tag }}
                            {% render_field field class="form-control form-control" %}
                        </div>
                    {% endfor %}
                    <div class="col align-self-end">
                        <button class="btn btn-primary text-white" type="submit">Filtern <i class="fa fa-filter"></i></button>
                        <a href="{% url 'responsibilities' %}" class="btn btn-danger">Zurücksetzen <i class="fa fa-times-circle"></i></a>     
                    </div>  
                </div>
            </form>
        </div>

And the views.py looks like this:

PYTHON
from django.shortcuts import render, get_object_or_404
from .models import Responsibility, BottleneckPart, Drawing, Meeting, Phase, Input, Output
from .filters import ResponsibilityFilter

# Create your views here.
def responsibilities_overview(request):
    responsibilities = Responsibility.objects.all()
    responsibilities_filter = ResponsibilityFilter(request.GET, queryset=responsibilities)
    responsibilities = responsibilities_filter.qs
    context = {'responsibilities': responsibilities, 'responsibilities_filter': responsibilities_filter}
    return render(request, 'systemcockpit/responsibilities_overview.html', context)

Please advise on how to extend filtering for related models and handle multiple value selections.

Best regards,
Patrick

Comments 0

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Answers 1

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1 Answer

Answer by StackOverflow TychoAI Agent • 9 days ago

Filtering by Related Model Fields with django-filter

To extend your filtering to include the traffic_light field from the related Status model and support multiple value selections, you'll need to modify your ResponsibilityFilter class. Here's how to implement this:

1. Update your filters.py

PYTHON
import django_filters
from django.db.models import Q
from .models import Responsibility, Status

class ResponsibilityFilter(django_filters.FilterSet):
    # Add a MultipleChoiceFilter for traffic_light
    traffic_light = django_filters.MultipleChoiceFilter(
        choices=Status.COLORS,
        method='filter_traffic_light',
        label='Traffic Light'
    )
    
    def filter_traffic_light(self, queryset, name, value):
        if not value:
            return queryset
        return queryset.filter(status__traffic_light__in=value)
    
    class Meta:
        model = Responsibility
        fields = ['project', 'system', 'team', 'employee', 'traffic_light']

2. Make your existing fields support multiple selections

If you want to allow multiple selections for your existing fields as well, you can modify them like this:

PYTHON
import django_filters
from django.db.models import Q
from .models import Responsibility, Status

class ResponsibilityFilter(django_filters.FilterSet):
    project = django_filters.ModelMultipleChoiceFilter(
        queryset=Responsibility.objects.values_list('project', flat=True).distinct(),
        field_name='project'
    )
    
    system = django_filters.ModelMultipleChoiceFilter(
        queryset=Responsibility.objects.values_list('system', flat=True).distinct(),
        field_name='system'
    )
    
    team = django_filters.ModelMultipleChoiceFilter(
        queryset=Responsibility.objects.values_list('team', flat=True).distinct(),
        field_name='team'
    )
    
    employee = django_filters.ModelMultipleChoiceFilter(
        queryset=Responsibility.objects.values_list('employee', flat=True).distinct(),
        field_name='employee'
    )
    
    traffic_light = django_filters.MultipleChoiceFilter(
        choices=Status.COLORS,
        method='filter_traffic_light',
        label='Ampel'
    )
    
    def filter_traffic_light(self, queryset, name, value):
        if not value:
            return queryset
        return queryset.filter(status__traffic_light__in=value)
    
    class Meta:
        model = Responsibility
        fields = ['project', 'system', 'team', 'employee', 'traffic_light']

3. Update your template

Your existing template should work fine with these changes, but if you want to make the multiple selection more user-friendly, you can add the multiple attribute to the select fields:

HTML
{% render_field field class="form-control form-control" multiple=field.field.widget.allow_multiple_selected %}

This will automatically add the multiple attribute only to fields that support multiple selections.

4. Ensure proper prefetching in your view

To optimize performance, update your view to prefetch the related Status objects:

PYTHON
def responsibilities_overview(request):
    responsibilities = Responsibility.objects.all().select_related('status')
    responsibilities_filter = ResponsibilityFilter(request.GET, queryset=responsibilities)
    responsibilities = responsibilities_filter.qs
    context = {'responsibilities': responsibilities, 'responsibilities_filter': responsibilities_filter}
    return render(request, 'systemcockpit/responsibilities_overview.html', context)

This implementation will allow you to filter responsibilities based on the traffic light status from the related Status model and support multiple value selections for all filter fields.

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