Django ORM处理多个多对多关系的方式 [英] Django ORM way of going through multiple Many-to-Many relationship

问题描述

亲爱的人们试图帮助他人，

Dear people trying to help others,

我正在尝试弄清楚如何让Django在不编写自定义SQL的情况下为我做连接。

I am trying to figure out how to get Django to do a join for me without writing custom SQL.

假设我有以下模型

class Parent(models.Model): 
  name =  models.CharField()
  children = models.ManyToManyField(Child, through="Parent_Child", related_name="parents")

class Parent_Child(models.Model):
  parent = models.ForeignKey(Parent, related_name='attached_children')
  child = models.ForeignKey(Child,  related_name='attached_parents')

class Child(models.Model): 
  name = models.CharField() 
  toys = models.ManyToManyField(Toy, hrough="Child_Toy", related_name="toy_owners")

class Child_Toy(models.Model): 
  child = models.ForeignKey(Child, related_name='attached_toys') 
  toy =  models.ForeignKey(Toy, related_name='toy_owner')

class Toy(models.Model): 
  name = models.CharField

父母可以有多个孩子。一个孩子可以有多个父母。一个孩子可以拥有多个玩具。玩具可以由多个孩子拥有。

A parent can have multiple children. A child can have multiple parents. A child can own multiple toys. Toys can be owned by multiple children.

我想获得父母子女拥有的所有玩具的列表。

I want to get a list of all toys owned by a Parent's Children.

因此，我可以执行以下操作：
parent.children.all（）
和 child.toys。 all（）

So, I can do things like: parent.children.all() and child.toys.all()

我想做的事情就像 parent.children.toys.all（）尝试执行此操作时，得到： AttributeError：'ManyRelatedManager'对象没有属性'toys'。我确实了解错误- parent.children 返回多个记录。这是预期的。我不知道是如何给Django提示，我希望它向其查询添加一个附加联接。

what I want to do is something like parent.children.toys.all() When I try to do this I get: AttributeError: 'ManyRelatedManager' object has no attribute 'toys'. I do understand the error - parent.children returns multiple records. This is expected. What I can't figure out is how to give Django the hint that I want it to add an additional join to its query.

有没有办法做到这一点？加入Django还是我需要转到自定义SQL才能做到这一点？

Is there a way I can do this join within Django or do I need to go to custom SQL in order to do this?

请注意：以上内容只是为了说明我的问题，我使用的实际模型并不相关。我的问题实际上是试图弄清楚如何在Django中通过多个M2M关系加入而不必求助于SQL。

Please Note: The above is just meant to illustrate my issue, the actual models that I am using aren't that relevant. My issue is really trying to figure out how to join through multiple M2M relationships in Django without having to resort to SQL.

我非常感谢您的帮助。谢谢！

I appreciate your help in advance. Thanks!

推荐答案

只需编写以下内容：

Toy.objects.filter(toy_owners__parents=parent)

这篇关于Django ORM处理多个多对多关系的方式的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！