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