django GAE中的数据库错误“MultiQuery不支持keys_only”

Question

我在django non-rel中使用djangoappengine。

class Subject(TimeStampedModel):

    class_room = models.ForeignKey( ClassRoom, related_name='class_subject')
    subject = models.CharField( max_length=255)
    tutor = models.ForeignKey( UserProfile, related_name='tutor')

    def __unicode__(self):
        return self.subject





def quick_delete_subject(request, classroom_id, subject_id):

    if request.method == 'GET':
        classroom = ClassRoom.objects.get(pk=classroom_id)
        school = classroom.school
        school_id = school.pk

    try:
        old_subject = Subject.objects.get(pk=subject_id)
        old_subject.delete()
    except:
        raise

    return HttpResponse('Deleted')

但是当我尝试删除视图中的主题对象时，我收到此错误。 奇怪的是，有时删除对象没有任何错误。

Django Version:     1.5.5
Exception Type:     DatabaseError
Exception Value:    MultiQuery does not support keys_only.