Fixed #7530, #7716 -- When using select_related() and encountering a NULL

    restricted = requested is not None

    index_end = index_start + len(klass._meta.fields)

    obj = klass(*row[index_start:index_end])

    fields = row[index_start:index_end]

    if not [x for x in fields if x is not None]:

        # If we only have a list of Nones, there was not related object.

        return None, index_end

    obj = klass(*fields)

    for f in klass._meta.fields:

        if not select_related_descend(f, restricted, requested):

            continue

"""

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

Regression tests for proper working of ForeignKey(null=True).

"""

from django.db import models

# 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).

# that come after the NULLs, or else data that should exist won't). Regression

# test for #7369.

>>> c = Comment.objects.select_related().get(id=1)

>>> c.post

<Post: First 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)]

>>> [(c.id, c.comment_text, c.post) for c in comments]

[(1, u'My first comment', <Post: First Post>), (2, u'My second comment', None)]

# Regression test for #7530, #7716.

>>> Comment.objects.select_related('post').filter(post__isnull=True)[0].post is None

True

"""}