如何使用“反向”的Django ManyToMany关系？ [英] How to use the 'reverse' of a Django ManyToMany relationship?

问题描述

我来自Rails背景，使用Django提供的关联方法有一些麻烦。我有两个模型（为简洁起见而被简化），如下所示：

  class User（models.Model） ：
 username = models.CharField（max_length = 100，unique = True）
 companies = models.ManyToManyField（'Company'，blank = True）
 
 class公司（型号。模型）：
 name = models.CharField（max_length = 255）
  

根据Django文档：

ManyToManyField的模型并不重要，但您应该将其放在其中一个模型中，而不是两个。

所以我明白，如果我有一个用户的实例，称为用户，我可以做：

  user.companies 
  

我的问题是我如何做相反的事情？如何获得属于公司实例的所有用户，假设公司：

  company.users＃这不工作！ 
  

做什么约会？我已阅读的文档并没有真正涵盖这一点。我需要协会工作的两种方式，所以我不能简单地将它从一个模型移动到另一个模型。

解决方案

  company.user_set.all（）
  

将返回一个用户属于特定公司的对象。默认情况下，您可以使用 modelname_set 来扭转关系，但是您可以重写此定义时提供 related_name 作为参数模型，即

  class User（models.Model）：
 companies = models.ManyToManyField（User，.. 。，related_name =users）
 
> company.users.all（）
  

这里是相关文档

I'm coming from a Rails background, and am having a bit of trouble making use of the "Association Methods" provided in Django. I have two models (which have been simplified for the sake of brevity), like so:

class User(models.Model):
    username = models.CharField(max_length=100, unique=True)
    companies = models.ManyToManyField('Company', blank=True)

class Company(models.Model):
    name = models.CharField(max_length=255)

According to the Django documentation:

"It doesn't matter which model has the ManyToManyField, but you should only put it in one of the models -- not both.".

So I understand that if I have an instance of a User, called user, I can do:

user.companies

My question is how do I do the reverse? How do I get all users that belong to a Company instance, let's say Company:

company.users # This doesn't work!

What's the convention to do this? The documentation that I've read doesn't really cover this. I need the association to work both ways, so I can't simply move it from one model to the other.

解决方案

company.user_set.all()

will return a QuerySet of User objects that belong to a particular company. By default you use modelname_set to reverse the relationship, but you can override this be providing a related_name as a parameter when defining the model, i.e.

class User(models.Model):
    companies = models.ManyToManyField(User, ..., related_name="users")

> company.users.all()

here is the relevant documentation

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