Using django-filter¶

Django-filter provides a simple way to filter down a queryset based on parameters a user provides. Say we have a Product model and we want to let our users filter which products they see on a list page.

The model¶

Let’s start with our model:

from django.db import models

class Product(models.Model):
    name = models.CharField(max_length=255)
    price = models.DecimalField()
    description = models.TextField()
    release_date = models.DateField()
    manufacturer = models.ForeignKey(Manufacturer)

The filter¶

We have a number of fields and we want to let our users filter based on the price or the release_date. We create a FilterSet for this:

import django_filters

class ProductFilter(django_filters.FilterSet):
    name = django_filters.CharFilter(lookup_expr='iexact')

    class Meta:
        model = Product
        fields = ['price', 'release_date']

As you can see this uses a very similar API to Django’s ModelForm. Just like with a ModelForm we can also override filters, or add new ones using a declarative syntax.

Declaring filters¶

The declarative syntax provides you with the most flexibility when creating filters, however it is fairly verbose. We’ll use the below example to outline the core filter arguments on a FilterSet:

class ProductFilter(django_filters.FilterSet):
    price = django_filters.NumberFilter()
    price__gt = django_filters.NumberFilter(name='price', lookup_expr='gt')
    price__lt = django_filters.NumberFilter(name='price', lookup_expr='lt')

    release_year = django_filters.NumberFilter(name='release_date', lookup_expr='year')
    release_year__gt = django_filters.NumberFilter(name='release_date', lookup_expr='year__gt')
    release_year__lt = django_filters.NumberFilter(name='release_date', lookup_expr='year__lt')

    manufacturer__name = django_filters.CharFilter(lookup_expr='icontains')

    class Meta:
        model = Product

There are two main arguments for filters:

name: The name of the model field to filter on. You can traverse “relationship paths” using Django’s __ syntax to filter fields on a related model. ex, manufacturer__name.
lookup_expr: The field lookup to use when filtering. Django’s __ syntax can again be used in order to support lookup transforms. ex, year__gte.

Together, the field name and lookup_expr represent a complete Django lookup expression. A detailed explanation of lookup expressions is provided in Django’s lookup reference. django-filter supports expressions containing both transforms and a final lookup for version 1.9 of Django and above. For Django version 1.8, transformed expressions are not supported.

Common declarative problems¶

Below are some of the common problem that occur when declaring filters. It is recommended that you do read this as it provides a more complete understanding on how filters work.

Filter `name` and `lookup_expr` not configured¶

While name and lookup_expr are optional, it is recommended that you specify them. By default, if name is not specified, the filter’s name on the filterset class will be used. Additionally, lookup_expr defaults to exact. The following is an example of a misconfigured price filter:

class ProductFilter(django_filters.FilterSet):
    price__gt = django_filters.NumberFilter()

The filter instance will have a field name of price__gt and an exact lookup type. Under the hood, this will incorrectly be resolved as:

Produce.objects.filter(price__gt__exact=value)

The above will most likely generate a FieldError. The correct configuration would be:

class ProductFilter(django_filters.FilterSet):
    price__gt = django_filters.NumberFilter(name='price', lookup_expr='gt')

Missing `lookup_expr` for text search filters¶

It’s quite common to forget to set the lookup expression for CharField and TextField and wonder why a search for “foo” does not return results for “foobar”. This is because the default lookup type is exact, but you probably want to perform an icontains lookup.

Filter and lookup expression mismatch (in, range, isnull)¶

It’s not always appropriate to directly match a filter to its model field’s type, as some lookups expect different types of values. This is a commonly found issue with in, range, and isnull lookups. Let’s look at the following product model:

class Product(models.Model):
    category = models.ForeignKey(Category, null=True)

Given that category is optional, it’s reasonable to want to enable a search for uncategorized products. The following is an incorrectly configured isnull filter:

class ProductFilter(django_filters.FilterSet):
    uncategorized = django_filters.NumberFilter(name='category', lookup_expr='isnull')

So what’s the issue? While the underlying column type for category is an integer, isnull lookups expect a boolean value. A NumberFilter however only validates numbers. Filters are not ‘expression aware’ and won’t change behavior based on their lookup_expr. You should use filters that match the data type of the lookup expression instead of the data type underlying model field. The following would correctly allow you to search for both uncategorized products and products for a set of categories:

class NumberInFilter(django_filters.BaseInFilter, django_filters.NumberFilter):
    pass

class ProductFilter(django_filters.FilterSet):
    categories = NumberInFilter(name='category', lookup_expr='in')
    uncategorized = django_filters.BooleanFilter(name='category', lookup_expr='isnull')

More info on constructing IN and RANGE csv filters.

Generating filters with Meta.fields¶

The FilterSet Meta class provides a fields attribute that can be used for easily specifying multiple filters without significant code duplication. The base syntax supports a list of multiple field names:

import django_filters

class ProductFilter(django_filters.FilterSet):
    class Meta:
        model = Product
        fields = ['price', 'release_date']

The above generates ‘exact’ lookups for both the ‘price’ and ‘release_date’ fields.

Additionally, a dictionary can be used to specify multiple lookup expressions for each field:

import django_filters

class ProductFilter(django_filters.FilterSet):
    class Meta:
        model = Product
        fields = {
            'price': ['lt', 'gt'],
            'release_date': ['exact', 'year__gt'],
        }

The above would generate ‘price__lt’, ‘price__gt’, ‘release_date’, and ‘release_date__year__gt’ filters.

Note

The filter lookup type ‘exact’ is an implicit default and therefore never added to a filter name. In the above example, the release date’s exact filter is ‘release_date’, not ‘release_date__exact’.

Items in the fields sequence in the Meta class may include “relationship paths” using Django’s __ syntax to filter on fields on a related model:

class ProductFilter(django_filters.FilterSet):
    class Meta:
        model = Product
        fields = ['manufacturer__country']

Overriding default filters¶

Like django.contrib.admin.ModelAdmin, it is possible to override default filters for all the models fields of the same kind using filter_overrides:

class ProductFilter(django_filters.FilterSet):
    filter_overrides = {
        models.CharField: {
            'filter_class': django_filters.CharFilter,
            'extra': lambda f: {
                'lookup_expr': 'icontains',
            },
        },
        models.BooleanField: {
            'filter_class': django_filters.BooleanFilter,
            'extra': lambda f: {
                'widget': 'forms.CheckboxInput',
            },
        },
    }

    class Meta:
        model = Product
        fields = {
            'name': ['exact'],
            'release_date': ['isnull'],
        }

Request-based filtering¶

The FilterSet may be initialized with an optional request argument. If a request object is passed, then you may access the request during filtering. This allows you to filter by properties on the request, such as the currently logged-in user or the Accepts-Languages header.

Filtering the primary `.qs`¶

To filter the primary queryset by the request object, simply override the FilterSet.qs property. For example, you could filter blog articles to only those that are published and those that are owned by the logged-in user (presumably the author’s draft articles).

class ArticleFilter(django_filters.FilterSet):

    class Meta:
        model = Article
        fields = [...]

    @property
    def qs(self):
        parent = super(ArticleFilter, self).qs
        return parent.filter(is_published=True) \
            | parent.filter(author=request.user)

Customize filtering with `Filter.method`¶

You can control the behavior of a filter by specifying a method to perform filtering. View more information in the method reference. Note that you may access the filterset’s properties, such as the request.

class F(django_filters.FilterSet):
    username = CharFilter(method='my_custom_filter')

    class Meta:
        model = User
        fields = ['username']

    def my_custom_filter(self, queryset, name, value):
        return queryset.filter(**{
            name: value,
        })

The view¶

Now we need to write a view:

def product_list(request):
    f = ProductFilter(request.GET, queryset=Product.objects.all())
    return render(request, 'my_app/template.html', {'filter': f})

If a queryset argument isn’t provided then all the items in the default manager of the model will be used.

If you want to access the filtered objects in your views, for example if you want to paginate them, you can do that. They are in f.qs

The URL conf¶

We need a URL pattern to call the view:

url(r'^list$', views.product_list)

The template¶

And lastly we need a template:

{% extends "base.html" %}

{% block content %}
    <form action="" method="get">
        {{ filter.form.as_p }}
        <input type="submit" />
    </form>
    {% for obj in filter.qs %}
        {{ obj.name }} - ${{ obj.price }}<br />
    {% endfor %}
{% endblock %}

And that’s all there is to it! The form attribute contains a normal Django form, and when we iterate over the FilterSet.qs we get the objects in the resulting queryset.

Generic view & configuration¶

In addition to the above usage there is also a class-based generic view included in django-filter, which lives at django_filters.views.FilterView. You must provide either a model or filterset_class argument, similar to ListView in Django itself:

# urls.py
from django.conf.urls import url
from django_filters.views import FilterView
from myapp.models import Product

urlpatterns = [
    url(r'^list/$', FilterView.as_view(model=Product)),
]

You must provide a template at <app>/<model>_filter.html which gets the context parameter filter. Additionally, the context will contain object_list which holds the filtered queryset.

A legacy functional generic view is still included in django-filter, although its use is deprecated. It can be found at django_filters.views.object_filter. You must provide the same arguments to it as the class based view:

# urls.py
from django.conf.urls import url
from django_filters.views import object_filter
from myapp.models import Product

urlpatterns = [
    url(r'^list/$', object_filter, {'model': Product}),
]

The needed template and its context variables will also be the same as the class-based view above.