Fixed #9308 -- Corrected the updated of nullable foreign key fields when...

            update_query = sql.UpdateQuery(cls, connection)

            for field, model in cls._meta.get_fields_with_model():

                if (field.rel and field.null and field.rel.to in seen_objs and

                        filter(lambda f: f.column == field.column,

                        filter(lambda f: f.column == field.rel.get_related_field().column,

                        field.rel.to._meta.fields)):

                    if model:

                        sql.UpdateQuery(model, connection).clear_related(field,

>>> o.keys()

[<class 'modeltests.delete.models.F'>, <class 'modeltests.delete.models.E'>]

# temporarily replace the UpdateQuery class to verify that E.f is actually nulled out first

>>> import django.db.models.sql

>>> class LoggingUpdateQuery(django.db.models.sql.UpdateQuery):

...     def clear_related(self, related_field, pk_list):

...         print "CLEARING FIELD",related_field.name

...         return super(LoggingUpdateQuery, self).clear_related(related_field, pk_list)

>>> original_class = django.db.models.sql.UpdateQuery

>>> django.db.models.sql.UpdateQuery = LoggingUpdateQuery

>>> e1.delete()

CLEARING FIELD f

>>> e2 = E()

>>> e2.save()

[<class 'modeltests.delete.models.F'>, <class 'modeltests.delete.models.E'>]

>>> f2.delete()

CLEARING FIELD f

# Put this back to normal

>>> django.db.models.sql.UpdateQuery = original_class

"""

}