使用自定义的 Manager

class CategoryManager(models.Manager):
    """
    A manager that adds an "active()" method for all active categories
    """
    def active(self):
        """
        Only categories that are active
        """
        return self.get_query_set().filter(active=True)


class CategoryBase(MPTTModel):
    """
    This base model includes the absolute bare bones fields and methods. One
    could simply subclass this model and do nothing else and it should work.
    """
    parent = TreeForeignKey(‘self‘,
        blank=True,
        null=True,
        related_name=‘children‘,
        verbose_name=_(‘parent‘))
    name = models.CharField(max_length=100, verbose_name=_(‘name‘))
    slug = models.SlugField(verbose_name=_(‘slug‘))
    active = models.BooleanField(default=True, verbose_name=_(‘active‘))

    objects = CategoryManager()
    tree = TreeManager()

    def save(self, *args, **kwargs):
        """
        While you can activate an item without activating its descendants,
        It doesn‘t make sense that you can deactivate an item and have its
        decendants remain active.
        """
        if not self.slug:
            self.slug = slugify(SLUG_TRANSLITERATOR(self.name))[:50]

        super(CategoryBase, self).save(*args, **kwargs)

        if not self.active:
            for item in self.get_descendants():
                if item.active != self.active:
                    item.active = self.active
                    item.save()

    def __unicode__(self):
        ancestors = self.get_ancestors()
        return ‘ > ‘.join([force_unicode(i.name) for i in ancestors] + [self.name, ])

    class Meta:
        abstract = True
        unique_together = (‘parent‘, ‘name‘)
        ordering = (‘tree_id‘, ‘lft‘)

    class MPTTMeta:
        order_insertion_by = ‘name‘

from django.db import models

class PublicArticleManager(models.Manager):
    def get_query_set(self):
        return super(PublicArticleManager, self).get_query_set().filter(public = True)

class Article(models.Model):
    #...
    public =  models.BooleanField(‘是否发表‘, default = False)

    objects = models.Manager()
    public_articles = PublicArticleManager()