多个注释中的 Django Count() [英] Django Count() in multiple annotations

问题描述

假设我有一个简单的论坛模型:

Say I have a simple forum model:

class User(models.Model):
    username = models.CharField(max_length=25)
    ...

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

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

现在说我想查看用户子集的每个用户有多少主题和帖子(例如，他们的用户名以ab"开头).

Now say I want to see how many topics and posts each users of subset of users has (e.g. their username starts with "ab").

因此，如果我对每个帖子和主题进行一次查询:

So if I do one query for each post and topic:

User.objects.filter(username_startswith="ab")
            .annotate(posts=Count('post'))
            .values_list("username","posts")

产量:

[('abe', 5),('abby', 12),...]

和

User.objects.filter(username_startswith="ab")
            .annotate(topics=Count('topic'))
            .values_list("username","topics")

产量:

[('abe', 2),('abby', 6),...]

然而，当我尝试对两者进行注释以获得一个列表时，我得到了一些奇怪的东西:

HOWEVER, when I try annotating both to get one list, I get something strange:

User.objects.filter(username_startswith="ab")
            .annotate(posts=Count('post'))
            .annotate(topics=Count('topic'))
            .values_list("username","posts", "topics")

产量:

[('abe', 10, 10),('abby', 72, 72),...]

为什么主题和帖子会成倍增加?我期待这个:

Why are the topics and posts multiplied together? I expected this:

[('abe', 5, 2),('abby', 12, 6),...]

获得正确列表的最佳方法是什么?

What would be the best way of getting the correct list?

推荐答案

我认为 Count('topics', distinct=True) 应该做正确的事.这将使用 COUNT(DISTINCT topic.id) 而不是 COUNT(topic.id) 以避免重复.

I think Count('topics', distinct=True) should do the right thing. That will use COUNT(DISTINCT topic.id) instead of COUNT(topic.id) to avoid duplicates.

User.objects.filter(
    username_startswith="ab").annotate(
    posts=Count('post', distinct=True)).annotate(
    topics=Count('topic', distinct=True)).values_list(
    "username","posts", "topics")

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