Django用不同的字段注释计数 [英] Django annotate count with a distinct field

问题描述

我有两个模型定义如下：

I have two models defined loosely like this:

class InformationUnit(models.Model):
    username = models.CharField(max_length=255)
    project = models.ForeignKey('Project')
    ...

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

现在，在一个视图中，我想注释所有InformationUnits属于一个项目，所以我这样做：

Now, in a view, I want to annotate all the InformationUnits that belong to a project, so I do this:

p = Project.objects.all().annotate(Count('informationunit')

哪些工作只是ok
此外，我想知道，在每个项目，有多少不同的'用户名'参与
那就是计算在组成一个项目的InformationUnits中有多少个不同的用户名
我已经尝试了以下的，但它只是计数的信息单元，不管用户名：

which works just ok Furthermore, I want to know, in each project, how many distinct 'username' participate. That is, count how many distinct 'username' are there in the InformationUnits that compose one project. I have tried the following, but it simply counts the number of InformationUnit, regardless of the username:

p = Project.objects.all().annotate(Count('informationunit__username')

请注意，用户名不是一个对象，它是一个字符串。有没有干净的方法来做到这一点，或者我应该创建一个基于循环和意大利面条代码的更复杂的代码：P

Note that username is not an object, it is a string. Is there a clean way to do this or should I create a more complicated code based on loops and spaghetti code :P

非常感谢！

推荐答案

计数可以采用 distinct ，如下所示：

Count can take a distinct argument, like so:

p = Project.objects.all().annotate(Count('informationunit__username', 
                                         distinct=True))

这似乎没有记录，但你可以在来源为Count。

This doesn't seem to be documented, but you can find it in the source for Count.

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