Django中使用 Closure Table 储存无限分级数据

框架(架构)  /  管理员 发布于 7年前   452

这篇文章给大家介绍Django中使用 Closure Table 储存无限分级数据，具体内容如下所述：

起步

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.nameclass 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.namedef 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 qsdef get_children(self): """获得直属下级""" qs = Category.objects.filter(descendants__ancestor=self, descendants__distance=1) return qsdef 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 qsdef get_parent(self): """分类仅有一个父节点""" parent = Category.objects.get(ancestors__descendant=self, ancestors__distance=1) return parentdef get_parents(self): """分类仅有一个父节点""" qs = Category.objects.filter(ancestors__descendant=self, ancestors__distance=1) return qsdef 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站的支持！