25. Reverse lookups

This example describes Django version 0.96. For the current example, go here.

This demonstrates the reverse lookup features of the database API.

Model source code

from django.db import models

class User(models.Model):
    name = models.CharField(maxlength=200)

    def __str__(self):
        return self.name

class Poll(models.Model):
    question = models.CharField(maxlength=200)
    creator = models.ForeignKey(User)

    def __str__(self):
        return self.question

class Choice(models.Model):
    name = models.CharField(maxlength=100)
    poll = models.ForeignKey(Poll, related_name="poll_choice")
    related_poll = models.ForeignKey(Poll, related_name="related_choice")

    def __str(self):
        return self.name

Sample API usage

This sample code assumes the above models have been saved in a file mysite/models.py.

>>> from mysite.models import User, Poll, Choice

>>> john = User(name="John Doe")
>>> john.save()
>>> jim = User(name="Jim Bo")
>>> jim.save()
>>> first_poll = Poll(question="What's the first question?", creator=john)
>>> first_poll.save()
>>> second_poll = Poll(question="What's the second question?", creator=jim)
>>> second_poll.save()
>>> new_choice = Choice(poll=first_poll, related_poll=second_poll, name="This is the answer.")
>>> new_choice.save()

>>> # Reverse lookups by field name:
>>> User.objects.get(poll__question__exact="What's the first question?")
<User: John Doe>
>>> User.objects.get(poll__question__exact="What's the second question?")
<User: Jim Bo>

>>> # Reverse lookups by related_name:
>>> Poll.objects.get(poll_choice__name__exact="This is the answer.")
<Poll: What's the first question?>
>>> Poll.objects.get(related_choice__name__exact="This is the answer.")
<Poll: What's the second question?>

>>> # If a related_name is given you can't use the field name instead:
>>> Poll.objects.get(choice__name__exact="This is the answer")
Traceback (most recent call last):
    ...
TypeError: Cannot resolve keyword 'choice' into field