Django中使用 Closure Table 储存无限分级数据

Django中使用 Closure Table 储存无限分级数据

起步

上一篇讨论了如何用数据库存储无限分级的数据。对于数据量大的情况（比如用户之间有邀请链，有点三级分销的意思），就要用到 closure table 的结构来进行存储。那么在 Django 中如何处理这个结构的模型呢？

定义模型

至少是要两个模型的，一个是存储分类，一个储存分类之间的关系：

class Category(models.Model):
  name = models.CharField(max_length=31)
  def __str__(self):
    return self.name
class CategoryRelation(models.Model):
  ancestor = models.ForeignKey(Category, null=True, related_name='ancestors', on_delete=models.SET_NULL, db_constraint=False, verbose_name='祖先')
  descendant = models.ForeignKey(Category,null=True, related_name='descendants', on_delete=models.SET_NULL,
                  db_constraint=False, verbose_name='子孙')
  distance = models.IntegerField()
  class Meta:
    unique_together = ("ancestor", "descendant")

数据操作

获得所有后代节点

class Category(models.Model):
  ...
  def get_descendants(self, include_self=False):
    """获得所有后代节点"""
    kw = {
      'descendants__ancestor' : self
    }
    if not include_self:
      kw['descendants__distance__gt'] = 0
    qs = Category.objects.filter(**kw).order_by('descendants__distance')
    return qs获得直属下级
class Category(models.Model):
  ...
  def get_children(self):
    """获得直属下级"""
    qs = Category.objects.filter(descendants__ancestor=self, descendants__distance=1)
    return qs

节点的移动

节点的移动是比较难的，在 [ https://www.percona.com/blog/2011/02/14/moving-subtrees-in-closure-table/][1 ] 中讲述了，利用django能够执行原生的sql语句进行：

def add_child(self, child):
    """将某个分类加入本分类，"""
    if CategoryRelation.objects.filter(ancestor=child, descendant=self).exists() \
        or CategoryRelation.objects.filter(ancestor=self, descendant=child, distance=1).exists():
      """child不能是self的祖先节点 or 它们已经是父子节点"""
      return
    # 如果表中不存在节点自身数据
    if not CategoryRelation.objects.filter(ancestor=child, descendant=child).exists():
      CategoryRelation.objects.create(ancestor=child, descendant=child, distance=0)
    table_name = CategoryRelation._meta.db_table
    cursor = connection.cursor()
    cursor.execute(f"""
      DELETE a
      FROM
        {table_name} AS a
      JOIN {table_name} AS d ON a.descendant_id = d.descendant_id
      LEFT JOIN {table_name} AS x ON x.ancestor_id = d.ancestor_id
      AND x.descendant_id = a.ancestor_id
      WHERE
        d.ancestor_id = {child.id}
      AND x.ancestor_id IS NULL;
    """)
    cursor.execute(f"""
    INSERT INTO {table_name} (ancestor_id, descendant_id, distance)
    SELECT supertree.ancestor_id, subtree.descendant_id,
    supertree.distance+subtree.distance+1
    FROM {table_name} AS supertree JOIN {table_name} AS subtree
    WHERE subtree.ancestor_id = {child.id}
    AND supertree.descendant_id = {self.id};
    """)

 节点删除

节点删除有两种操作，一个是将所有子节点也删除，另一个是将自己点移到上级节点中。

扩展阅读

[ https://www.percona.com/blog/2011/02/14/moving-subtrees-in-closure-table/][2 ]
[ http://technobytz.com/closure_table_store_hierarchical_data.html][3 ]

完整代码

class Category(models.Model):
name = models.CharField(max_length=31)
def __str__(self):
  return self.name
def get_descendants(self, include_self=False):
  """获得所有后代节点"""
  kw = {
    'descendants__ancestor' : self
  }
  if not include_self:
    kw['descendants__distance__gt'] = 0
  qs = Category.objects.filter(**kw).order_by('descendants__distance')
  return qs
def get_children(self):
  """获得直属下级"""
  qs = Category.objects.filter(descendants__ancestor=self, descendants__distance=1)
  return qs
def get_ancestors(self, include_self=False):
  """获得所有祖先节点"""
  kw = {
    'ancestors__descendant': self
  }
  if not include_self:
    kw['ancestors__distance__gt'] = 0
  qs = Category.objects.filter(**kw).order_by('ancestors__distance')
  return qs
def get_parent(self):
  """分类仅有一个父节点"""
  parent = Category.objects.get(ancestors__descendant=self, ancestors__distance=1)
  return parent
def get_parents(self):
  """分类仅有一个父节点"""
  qs = Category.objects.filter(ancestors__descendant=self, ancestors__distance=1)
  return qs
def remove(self, delete_subtree=False):
  """删除节点"""
  if delete_subtree:
    # 删除所有子节点
    children_queryset = self.get_descendants(include_self=True)
    for child in children_queryset:
      CategoryRelation.objects.filter(Q(ancestor=child) | Q(descendant=child)).delete()
      child.delete()
  else:
    # 所有子节点移到上级
    parent = self.get_parent()
    children = self.get_children()
    for child in children:
      parent.add_chile(child)
    # CategoryRelation.objects.filter(descendant=self, distance=0).delete()
    CategoryRelation.objects.filter(Q(ancestor=self) | Q(descendant=self)).delete()
    self.delete()
def add_child(self, child):
  """将某个分类加入本分类，"""
  if CategoryRelation.objects.filter(ancestor=child, descendant=self).exists() \
      or CategoryRelation.objects.filter(ancestor=self, descendant=child, distance=1).exists():
    """child不能是self的祖先节点 or 它们已经是父子节点"""
    return
  # 如果表中不存在节点自身数据
  if not CategoryRelation.objects.filter(ancestor=child, descendant=child).exists():
    CategoryRelation.objects.create(ancestor=child, descendant=child, distance=0)
  table_name = CategoryRelation._meta.db_table
  cursor = connection.cursor()
  cursor.execute(f"""
    DELETE a
    FROM
      {table_name} AS a
    JOIN {table_name} AS d ON a.descendant_id = d.descendant_id
    LEFT JOIN {table_name} AS x ON x.ancestor_id = d.ancestor_id
    AND x.descendant_id = a.ancestor_id
    WHERE
      d.ancestor_id = {child.id}
    AND x.ancestor_id IS NULL;
  """)
  cursor.execute(f"""
  INSERT INTO {table_name} (ancestor_id, descendant_id, distance)
  SELECT supertree.ancestor_id, subtree.descendant_id,
  supertree.distance+subtree.distance+1
  FROM {table_name} AS supertree JOIN {table_name} AS subtree
  WHERE subtree.ancestor_id = {child.id}
  AND supertree.descendant_id = {self.id};
  """)class CategoryRelation(models.Model): ancestor = models.ForeignKey(Category, null=True, related_name='ancestors', on_delete=models.SET_NULL, db_constraint=False, verbose_name='祖先') descendant = models.ForeignKey(Category,null=True, related_name='descendants', on_delete=models.SET_NULL, db_constraint=False, verbose_name='子孙') distance = models.IntegerField()
class Meta:
  unique_together = ("ancestor", "descendant")[1]: https://www.percona.com/blog/2011/02/14/moving-subtrees-in-closure-table/
 [2]: https://www.percona.com/blog/2011/02/14/moving-subtrees-in-closure-table/
 [3]: http://technobytz.com/closure_table_store_hierarchical_data.html

总结

以上所述是小编给大家介绍的Django中使用 Closure Table 储存无限分级数据，希望对大家有所帮助，如果大家有任何疑问请给我留言，小编会及时回复大家的。在此也非常感谢大家对我们网站的支持！