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Django中使用 Closure Table 儲存無限分級數(shù)據(jù)

更新時間：2019年06月06日 14:20:52 作者：棲遲于一丘

對于數(shù)據(jù)量大的情況（比如用戶之間有邀請鏈，有點三級分銷的意思），就要用到 closure table 的結(jié)構(gòu)來進(jìn)行存儲。這篇文章主要介紹了Django中使用 Closure Table 儲存無限分級數(shù)據(jù),需要的朋友可以參考下

這篇文章給大家介紹Django中使用 Closure Table 儲存無限分級數(shù)據(jù)，具體內(nèi)容如下所述：

起步

對于數(shù)據(jù)量大的情況（比如用戶之間有邀請鏈，有點三級分銷的意思），就要用到 closure table 的結(jié)構(gòu)來進(jìn)行存儲。那么在 Django 中如何處理這個結(jié)構(gòu)的模型呢？

定義模型

至少是要兩個模型的，一個是存儲分類，一個儲存分類之間的關(guān)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='子孫')
 distance = models.IntegerField()
 class Meta:
 unique_together = ("ancestor", "descendant")

數(shù)據(jù)操作

獲得所有后代節(jié)點

class Category(models.Model):
 ...
 def get_descendants(self, include_self=False):
 """獲得所有后代節(jié)點"""
 kw = {
 'descendants__ancestor' : self
 }
 if not include_self:
 kw['descendants__distance__gt'] = 0
 qs = Category.objects.filter(**kw).order_by('descendants__distance')
 return qs獲得直屬下級
class Category(models.Model):
 ...
 def get_children(self):
 """獲得直屬下級"""
 qs = Category.objects.filter(descendants__ancestor=self, descendants__distance=1)
 return qs

節(jié)點的移動

節(jié)點的移動是比較難的，在 [ https://www.percona.com/blog/2011/02/14/moving-subtrees-in-closure-table/][1 ] 中講述了，利用django能夠執(zhí)行原生的sql語句進(jìn)行：

def add_child(self, child):
 """將某個分類加入本分類，"""
 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的祖先節(jié)點 or 它們已經(jīng)是父子節(jié)點"""
 return
 # 如果表中不存在節(jié)點自身數(shù)據(jù)
 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};
 """)

節(jié)點刪除

節(jié)點刪除有兩種操作，一個是將所有子節(jié)點也刪除，另一個是將自己點移到上級節(jié)點中。

擴(kuò)展閱讀

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

完整代碼

class Category(models.Model):
name = models.CharField(max_length=31)
def __str__(self):
 return self.name
def get_descendants(self, include_self=False):
 """獲得所有后代節(jié)點"""
 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):
 """獲得直屬下級"""
 qs = Category.objects.filter(descendants__ancestor=self, descendants__distance=1)
 return qs
def get_ancestors(self, include_self=False):
 """獲得所有祖先節(jié)點"""
 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):
 """分類僅有一個父節(jié)點"""
 parent = Category.objects.get(ancestors__descendant=self, ancestors__distance=1)
 return parent
def get_parents(self):
 """分類僅有一個父節(jié)點"""
 qs = Category.objects.filter(ancestors__descendant=self, ancestors__distance=1)
 return qs
def remove(self, delete_subtree=False):
 """刪除節(jié)點"""
 if delete_subtree:
 # 刪除所有子節(jié)點
 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:
 # 所有子節(jié)點移到上級
 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):
 """將某個分類加入本分類，"""
 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的祖先節(jié)點 or 它們已經(jīng)是父子節(jié)點"""
 return
 # 如果表中不存在節(jié)點自身數(shù)據(jù)
 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='子孫') 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

總結(jié)

以上所述是小編給大家介紹的Django中使用 Closure Table 儲存無限分級數(shù)據(jù)，希望對大家有所幫助，如果大家有任何疑問請給我留言，小編會及時回復(fù)大家的。在此也非常感謝大家對腳本之家網(wǎng)站的支持！

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