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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. 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)
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):
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 overide filters, or add new ones using a
declarative syntax::
import django_filters
class ProductFilter(django_filters.FilterSet):
price = django_filters.NumberFilter(lookup_type='lt')
class Meta:
model = Product
fields = ['price', 'release_date']
Filters take a ``lookup_type`` argument which specifies what lookup type to
use with Django's ORM. So here when a user entered a price it would show all
Products with a price less than that.
Filters also take any arbitrary keyword arguments which get passed onto the
``django.forms.Field`` constructor. These extra keyword arguments get stored
in ``Filter.extra``, so it's possible to overide the constructor of a
``FilterSet`` to add extra ones::
class ProductFilterSet(django_filters.FilterSet):
class Meta:
model = Product
fields = ['manufacturer']
def __init__(self, *args, **kwargs):
super(ProductFilterSet, self).__init__(*args, **kwargs)
self.filters['manufacturer'].extra.update(
{'empty_label': u'All Manufacturers'})
Now we need to write a view::
def product_list(request):
f = ProductFilter(request.GET, queryset=Product.objects.all())
return render_to_response('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.
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 %}
{{ obj.name }} - ${{ obj.price }}<br />
{% endfor %}
{% endblock %}
And that's all there is to it! The ``form`` attribute contains a normal
Django form, and when we iterate over the ``FilterSet`` we get the objects in
the resulting queryset.
You can also allow the user to control ordering, this is done by providing the
``order_by`` argument in the Filter's Meta class. ``order_by`` can be either a
``list`` or ``tuple`` of field names, in which case those are the options, or
it can be a ``bool`` which, if True, indicates that all fields that
the user can filter on can also be sorted on.
Note that the default query parameter name used for ordering is ``o``. You
can override this by setting an ``order_by_field`` attribute on the
``FilterSet`` class to the string value you would like to use.
The inner ``Meta`` class also takes an optional ``form`` argument. This is a
form class from which ``FilterSet.form`` will subclass. This works similar to
the ``form`` option on a ``ModelAdmin.``
Items in the ``fields`` sequence in the ``Meta`` class may include
"relationship paths" using Django's ``__`` syntax to filter on fields on a
related model.
If you want to use a custom widget, or in any other way overide the ordering
field you can overide the ``get_ordering_field()`` method on a ``FilterSet``.
This method just needs to return a Form Field.
Generic View
============
In addition to the above usage there is also a generic view included in
django-filter, which lives at ``django_filters.views.object_filter``. You must
provide either a ``model`` or ``filter_class`` argument, similar to the
``create_update`` view in Django itself::
url(r'^list/$',
'django_filters.views.object_filter',
{'model': Product}),
You must provide a template at ``<app>/<model>_filter.html`` which gets the
context parameter ``filter``.
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