--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/thirdparty/google_appengine/lib/django/tests/modeltests/many_to_one_null/models.py	Tue Aug 26 21:49:54 2008 +0000
@@ -0,0 +1,124 @@
+"""
+16. Many-to-one relationships that can be null
+
+To define a many-to-one relationship that can have a null foreign key, use
+``ForeignKey()`` with ``null=True`` .
+"""
+
+from django.db import models
+
+class Reporter(models.Model):
+    name = models.CharField(maxlength=30)
+
+    def __str__(self):
+        return self.name
+
+class Article(models.Model):
+    headline = models.CharField(maxlength=100)
+    reporter = models.ForeignKey(Reporter, null=True)
+
+    class Meta:
+        ordering = ('headline',)
+
+    def __str__(self):
+        return self.headline
+
+__test__ = {'API_TESTS':"""
+# Create a Reporter.
+>>> r = Reporter(name='John Smith')
+>>> r.save()
+
+# Create an Article.
+>>> a = Article(headline="First", reporter=r)
+>>> a.save()
+
+>>> a.reporter.id
+1
+
+>>> a.reporter
+<Reporter: John Smith>
+
+# Article objects have access to their related Reporter objects.
+>>> r = a.reporter
+
+# Create an Article via the Reporter object.
+>>> a2 = r.article_set.create(headline="Second")
+>>> a2
+<Article: Second>
+>>> a2.reporter.id
+1
+
+# Reporter objects have access to their related Article objects.
+>>> r.article_set.all()
+[<Article: First>, <Article: Second>]
+>>> r.article_set.filter(headline__startswith='Fir')
+[<Article: First>]
+>>> r.article_set.count()
+2
+
+# Create an Article with no Reporter by passing "reporter=None".
+>>> a3 = Article(headline="Third", reporter=None)
+>>> a3.save()
+>>> a3.id
+3
+>>> print a3.reporter
+None
+
+# Need to reget a3 to refresh the cache
+>>> a3 = Article.objects.get(pk=3)
+>>> print a3.reporter.id
+Traceback (most recent call last):
+    ...
+AttributeError: 'NoneType' object has no attribute 'id'
+
+# Accessing an article's 'reporter' attribute returns None
+# if the reporter is set to None.
+>>> print a3.reporter
+None
+
+# To retrieve the articles with no reporters set, use "reporter__isnull=True".
+>>> Article.objects.filter(reporter__isnull=True)
+[<Article: Third>]
+
+# Set the reporter for the Third article
+>>> r.article_set.add(a3)
+>>> r.article_set.all()
+[<Article: First>, <Article: Second>, <Article: Third>]
+
+# Remove an article from the set, and check that it was removed.
+>>> r.article_set.remove(a3)
+>>> r.article_set.all()
+[<Article: First>, <Article: Second>]
+>>> Article.objects.filter(reporter__isnull=True)
+[<Article: Third>]
+
+# Create another article and reporter
+>>> r2 = Reporter(name='Paul Jones')
+>>> r2.save()
+>>> a4 = r2.article_set.create(headline='Fourth')
+>>> r2.article_set.all()
+[<Article: Fourth>]
+
+# Try to remove a4 from a set it does not belong to
+>>> r.article_set.remove(a4)
+Traceback (most recent call last):
+...
+DoesNotExist: <Article: Fourth> is not related to <Reporter: John Smith>.
+
+>>> r2.article_set.all()
+[<Article: Fourth>]
+
+# Use descriptor assignment to allocate ForeignKey. Null is legal, so
+# existing members of set that are not in the assignment set are set null
+>>> r2.article_set = [a2, a3]
+>>> r2.article_set.all()
+[<Article: Second>, <Article: Third>]
+
+# Clear the rest of the set
+>>> r.article_set.clear()
+>>> r.article_set.all()
+[]
+>>> Article.objects.filter(reporter__isnull=True)
+[<Article: First>, <Article: Fourth>]
+
+"""}