Django：查询所有具有外键指向的项目 [英] Django: query all items that have a foreign key point to them

问题描述

我有两个模型：

class A(models.Model):
    name = models.CharField(max_length=100, unique=True)

class B(models.Model):
    a = models.ForeignKey(A)

在Django中，我如何选择所有具有指向对象的 B类对象的 A类对象？例如，如果数据库包含 A类的以下三个条目：

In Django, how can I select all objects of class 'A' that have an object of class B that points to them? For example, if the database contains these three entries of class 'A':

A, named "one"
A, named "two"
A, named "three"

B：

B, points to "two"
B, points to "three"

我要选择类型A的两个和三个类。

I want to select classes "two" and "three" of type A.

推荐答案

您可以这样做：

a_qs = A.objects.filter(b = b) 

其中b是 B类的对象和 b = 表示要查询反向关系的小写模型名称。

where b is an object of class B and the b= refers to the lowercase model name which you want to query the reverse relationship.

有关在此处跨越关系的查找。它涵盖了如何对模型的ForeignKey属性进行反向查找

Read more on lookups that span relationships here. It covers how to do a reverse lookup on models' ForeignKey attributes

编辑：

如果您正在寻找所有没有的对象都指向任何 ForeignKey 对象，可以使用 排除 和 __ isnull

If you are looking for all objects which do not have any ForeignKey objects pointing to them, you can use exclude and __isnull

a_qs = A.objects.exclude(b__isnull = True) 

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