在 Django QuerySet 中，如何过滤“不存在"?在多对一的关系中 [英] In a Django QuerySet, how to filter for "not exists" in a many-to-one relationship

问题描述

我有两个这样的模型:

class User(models.Model):
    email = models.EmailField()

class Report(models.Model):
    user = models.ForeignKey(User)

实际上，每个模型都有更多的字段，这些字段与这个问题无关.

In reality each model has more fields which are of no consequence to this question.

我想过滤所有拥有以a"开头且没有报告的电子邮件的用户.将有更多基于其他字段的 .filter() 和 .exclude() 条件.

I want to filter all users who have an email which starts with 'a' and have no reports. There will be more .filter() and .exclude() criteria based on other fields.

我想这样处理:

users = User.objects.filter(email__like = 'a%')

users = users.filter(<other filters>)

users = ???

我想要???过滤掉没有关联报告的用户.我该怎么做?如果这不可能如我所介绍的那样，有什么替代方法?

I would like ??? to filter out users who do not have reports associated with them. How would I do this? If this is not possible as I have presented it, what is an alternate approach?

推荐答案

注意:这个答案是在 2013 年为 Django 1.5 编写的.有关适用于较新版本 Django 的更好方法，请参阅其他答案

使用 isnull.

users_without_reports = User.objects.filter(report__isnull=True)
users_with_reports = User.objects.filter(report__isnull=False).distinct()

当您使用 isnull=False 时，需要 distinct() 以防止重复结果.

When you use isnull=False, the distinct() is required to prevent duplicate results.

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