from django.db import models

class Poll(models.Model):

    question = models.CharField(maxlength=200)

    def __str__(self):

        return "Q: %s " % self.question

class Choice(models.Model):

    poll = models.ForeignKey(Poll)

    choice = models.CharField(maxlength=200)

    def __str__(self):

        return "Choice: %s in poll %s" % (self.choice, self.poll)

__test__ = {'API_TESTS':"""

# Regression test for the use of None as a query value. None is interpreted as 

# an SQL NULL, but only in __exact queries.

# Set up some initial polls and choices

>>> p1 = Poll(question='Why?')

>>> p1.save()

>>> c1 = Choice(poll=p1, choice='Because.')

>>> c1.save()

>>> c2 = Choice(poll=p1, choice='Why Not?')

>>> c2.save()

# Exact query with value None returns nothing (=NULL in sql)

>>> Choice.objects.filter(id__exact=None)

[]

# Valid query, but fails because foo isn't a keyword

>>> Choice.objects.filter(foo__exact=None) 

Traceback (most recent call last):

...

TypeError: Cannot resolve keyword 'foo' into field

# Can't use None on anything other than __exact

>>> Choice.objects.filter(id__gt=None)

Traceback (most recent call last):

...

ValueError: Cannot use None as a query value

# Can't use None on anything other than __exact

>>> Choice.objects.filter(foo__gt=None)

Traceback (most recent call last):

...

ValueError: Cannot use None as a query value

# Related managers use __exact=None implicitly if the object hasn't been saved.

>>> p2 = Poll(question="How?")

>>> p2.choice_set.all()

[]

"""}