Fixes #2737 -- Added code to allow None as a query value for __exact queries, raising an error otherwise. __exact=None is interpreted as the SQL 'value = NULL'. This fixes some minor problems with queries on unsaved objects with related object sets, and stops queries with a value of None being outright ignored (even if they reference an unknown attribute).

git-svn-id: http://code.djangoproject.com/svn/django/trunk@3902 bcc190cf-cafb-0310-a4f2-bffc1f526a37

tests/regressiontests/null_queries/models.py

@@ -0,0 +1,54 @@
+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()
+[]
+
+"""}