Fixed #7369: fixed a corner-case involving select_related() following non-null FKs after null ones. Thanks, George Vilches

git-svn-id: http://code.djangoproject.com/svn/django/trunk@7597 bcc190cf-cafb-0310-a4f2-bffc1f526a37

tests/regressiontests/null_fk/models.py

@@ -0,0 +1,55 @@
+"""
+Regression tests for proper working of ForeignKey(null=True). Tests these bugs:
+
+    * #7369: FK non-null after null relationship on select_related() generates an invalid query
+
+"""
+
+from django.db import models
+
+class SystemInfo(models.Model):
+    system_name = models.CharField(max_length=32)
+
+class Forum(models.Model):
+    system_info = models.ForeignKey(SystemInfo)
+    forum_name = models.CharField(max_length=32)
+
+class Post(models.Model):
+    forum = models.ForeignKey(Forum, null=True)
+    title = models.CharField(max_length=32)
+
+    def __unicode__(self):
+        return self.title
+
+class Comment(models.Model):
+    post = models.ForeignKey(Post, null=True)
+    comment_text = models.CharField(max_length=250)
+
+    def __unicode__(self):
+        return self.comment_text
+
+__test__ = {'API_TESTS':"""
+
+>>> s = SystemInfo.objects.create(system_name='First forum')
+>>> f = Forum.objects.create(system_info=s, forum_name='First forum')
+>>> p = Post.objects.create(forum=f, title='First Post')
+>>> c1 = Comment.objects.create(post=p, comment_text='My first comment')
+>>> c2 = Comment.objects.create(comment_text='My second comment')
+
+# Starting from comment, make sure that a .select_related(...) with a specified
+# set of fields will properly LEFT JOIN multiple levels of NULLs (and the things
+# that come after the NULLs, or else data that should exist won't).
+>>> c = Comment.objects.select_related().get(id=1)
+>>> c.post
+<Post: First Post>
+>>> c = Comment.objects.select_related().get(id=2)
+>>> print c.post
+None
+
+>>> comments = Comment.objects.select_related('post__forum__system_info').all()
+>>> [(c.id, c.post.id) for c in comments]
+[(1, 1), (2, None)]
+>>> [(c.comment_text, c.post.title) for c in comments]
+[(u'My first comment', u'First Post'), (u'My second comment', None)]
+
+"""}