Getting Started

Django-property-filter provides extended functionality to django-filter to allow filtering by class properties by providing new Sub Classes to django-filter’s Filter and Filterset classes.

All existing django-filter functionality is still working as before.

Example Model

Our Model:

from django.db import models

class BookSeries(models.Model):
    name = models.CharField(max_length=255)

    @property
    def book_count(self):
      return Book.objects.filter(series=self).count()

class Book(models.Model):
    title = models.CharField(max_length=255)
    price = models.DecimalField()
    discount_percentage = models.IntegerField()
    author = models.TextField()
    series = models.ForeignKey(BookSeries)

    @property
    def discounted_price(self):
      return self.price * self.discount_percentage / 100

Implicit Filter Creation

If we want to filter by discounted price as well as number of books in a series, which both are properties and not fields in the database, we would do the following.:

from django_property_filter import (
  PropertyFilterSet,
  PropertyNumberFilter
)

class BookFilterSet(PropertyFilterSet):

  class Meta:
      model = Book
      exclude = ['price']
      property_fields = [
        ('discounted_price', PropertyNumberFilter, ['lt', 'exact']),
        ('series.book_count.', PropertyNumberFilter, ['gt', 'exact']),
      ]

This will create 4 Filters

1.) A “less than” and an “exact” filter for the “discounted_price” property

of the Book Model

2.) A “greater than” and an “exact” filter for the “book_count” property

of the related Model “series”.

The order in which the property filters are applied are in the same order as they are defined. In the above filter will be in order of:

1.) discounted_price: lt
2.) discounted_price: exact
3.) series.book_count: gt
4.) series.book_count: exact

This can be usefull to speed up the filtering by property filters if filters are defined first that are likely to filter a large number of values. E.g. a boolean field might be filtering an average of half the values, while a field representing a name will likely filter fewer.

Since PropertyFilterSet is and extension to django-filter’s Filterset which requires either the Meta attribute “fields” or “exclude” to be set we excluded the “price” field. If we had instead used:

fields = ['price']

It would also have created an “exact” filter for the book price.

The only difference to using a normal FilterSet from django-filter is the “property_fields” field.

The “property_fields” is a list of tuples with 3 values.

1.) The property name.

If the property is on a related Model it should be separated by “__”, and can span multiple levels e.g. fk__fk__fk__property

2.) The specific Property Filter to use.

This is necessary since it can’t be determined what the return type of the property will be in all cases

3.) The list of lookup expressions.

Explicit Filter Creation

It is also possible to create Filters explicitely:

from django_property_filter import PropertyNumberFilter, PropertyFilterSet

class BookFilterSet(PropertyFilterSet):
    prop_number_gte = PropertyNumberFilter(field_name='discounted_price', lookup_expr='gte')
    prop_number_lt = PropertyNumberFilter(field_name='discounted_price', lookup_expr='lt')

    class Meta:
        model = NumberClass
        fields = ['prop_number_gte', 'prop_number_lt']

This creates a “greater than or equel” and a “less than” filter for the discounted_price property.

The order in which the property filters are applied are in the same order as they are defined. In the above filter will be in order of:

1.) prop_number_gte
2.) prop_number_lt

This can be usefull to speed up the filtering by property filters if filters are defined first that are likely to filter a large number of values. E.g. a boolean field might be filtering an average of half the values, while a field representing a name will likely filter fewer.