Improved table join handling for comparisons against NULL.

                field, source, opts, join_list, last, _ = query.setup_joins(

                    field_list, query.get_meta(),

                    query.get_initial_alias(), False)

                _, _, col, _, join_list = query.trim_joins(source, join_list, last, False)

                col, _, join_list = query.trim_joins(source, join_list, last, False)

                self.cols[node] = (join_list[-1], col)

            except FieldDoesNotExist:

                field_list, opts, self.get_initial_alias(), False)

            # Process the join chain to see if it can be trimmed

            _, _, col, _, join_list = self.trim_joins(source, join_list, last, False)

            col, _, join_list = self.trim_joins(source, join_list, last, False)

            # If the aggregate references a model or field that requires a join,

            # those joins must be LEFT OUTER - empty join rows must be returned

                    can_reuse)

            return

        # Process the join chain to see if it can be trimmed

        final, penultimate, col, alias, join_list = self.trim_joins(target, join_list, last, trim)

        if (lookup_type == 'isnull' and value is True and not negate and

                final > 1):

            # If the comparison is against NULL, we need to use a left outer

            # join when connecting to the previous model. We make that

            # adjustment here. We don't do this unless needed as it's less

            # efficient at the database level.

            self.promote_alias(join_list[penultimate])

                len(join_list) > 1):

            # If the comparison is against NULL, we may need to use some left

            # outer joins when creating the join chain. This is only done when

            # needed, as it's less efficient at the database level.

            self.promote_alias_chain(join_list)

        # Process the join list to see if we can remove any inner joins from

        # the far end (fewer tables in a query is better).

        col, alias, join_list = self.trim_joins(target, join_list, last, trim)

        if connector == OR:

            # Some joins may need to be promoted when adding a new filter to a

        if negate:

            self.promote_alias_chain(join_list)

            if lookup_type != 'isnull':

                if final > 1:

                if len(join_list) > 1:

                    for alias in join_list:

                        if self.alias_map[alias][JOIN_TYPE] == self.LOUTER:

                            j_col = self.alias_map[alias][RHS_JOIN_COL]

        return field, target, opts, joins, last, extra_filters

    def trim_joins(self, target, join_list, last, trim):

        """An optimization: if the final join is against the same column as

        we are comparing against, we can go back one step in a join

        chain and compare against the LHS of the join instead (and then

        repeat the optimization). The result, potentially, involves less

        table joins.

        """

        Sometimes joins at the end of a multi-table sequence can be trimmed. If

        the final join is against the same column as we are comparing against,

        and is an inner join, we can go back one step in a join chain and

        compare against the LHS of the join instead (and then repeat the

        optimization). The result, potentially, involves less table joins.

        Returns a tuple

        The 'target' parameter is the final field being joined to, 'join_list'

        is the full list of join aliases.

        The 'last' list contains offsets into 'join_list', corresponding to

        each component of the filter.  Many-to-many relations, for example, add

        two tables to the join list and we want to deal with both tables the

        same way, so 'last' has an entry for the first of the two tables and

        then the table immediately after the second table, in that case.

        The 'trim' parameter forces the final piece of the join list to be

        trimmed before anything. See the documentation of add_filter() for

        details about this.

        Returns the final active column and table alias and the new active

        join_list.

        """

        final = len(join_list)

        penultimate = last.pop()

        alias = join_list[-1]

        while final > 1:

            join = self.alias_map[alias]

            if col != join[RHS_JOIN_COL]:

            if col != join[RHS_JOIN_COL] or join[JOIN_TYPE] != self.INNER:

                break

            self.unref_alias(alias)

            alias = join[LHS_ALIAS]

            final -= 1

            if final == penultimate:

                penultimate = last.pop()

        return final, penultimate, col, alias, join_list

        return col, alias, join_list

    def update_dupe_avoidance(self, opts, col, alias):

        """

    def __unicode__(self):

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

# A set of models with an inner one pointing to two outer ones.

class OuterA(models.Model):

    pass

class OuterB(models.Model):

    data = models.CharField(max_length=10)

class Inner(models.Model):

    first = models.ForeignKey(OuterA)

    second = models.ForeignKey(OuterB, null=True)

__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.

>>> p2.choice_set.all()

[]

# Querying across reverse relations and then another relation should insert

# outer joins correctly so as not to exclude results.

>>> obj = OuterA.objects.create()

>>> OuterA.objects.filter(inner__second=None)

[<OuterA: OuterA object>]

>>> OuterA.objects.filter(inner__second__data=None)

[<OuterA: OuterA object>]

>>> _ = Inner.objects.create(first=obj)

>>> Inner.objects.filter(first__inner__second=None)

[<Inner: Inner object>]

"""}

    def __unicode__(self):

        return u"Favorites for %s" % self.name

class Target(models.Model):

    pass

class Pointer(models.Model):

    other = models.OneToOneField(Target, primary_key=True)

class Pointer2(models.Model):

    other = models.OneToOneField(Target)

__test__ = {'API_TESTS':"""

# Regression test for #1064 and #1506: Check that we create models via the m2m

# relation if the remote model has a OneToOneField.

>>> r.place == p

True

# Regression test for #9968: filtering reverse one-to-one relations with

# primary_key=True was misbehaving. We test both (primary_key=True & False)

# cases here to prevent any reappearance of the problem.

>>> _ = Target.objects.create()

>>> Target.objects.filter(pointer=None)

[<Target: Target object>]

>>> Target.objects.exclude(pointer=None)

[]

>>> Target.objects.filter(pointer2=None)

[<Target: Target object>]

>>> Target.objects.exclude(pointer2=None)

[]

"""}