[英]How to count total occurrence of distinct field of same model in django?
I am trying to get the total count of occurrence of a field in same model in django. 我正在尝试在django中获取同一模型中某个字段发生的总数。 Is it possible to do it or not? 有可能做到吗?
for example I have a model as below: 例如我有一个如下模型:
class Blog(DateTimeModel):
title = models.CharField(max_length=255)
description = models.TextField()
category = models.CharField(max_length=255, null=True, blank=True)
and a table of data as below: 数据表如下:
id | title | description | category
----+-------------------------------------+----------------------+----------
1 | blog title first | description 1 | social
2 | blog title second | description 2 | social
3 | blog title third | description 3 | community
4 | blog title fourth | description 4 | community
5 | blog title fifth | description 5 | people
I want a result to be as: 我希望结果是:
<QuerySet [{'category': 'social', 'blog_count': '2'}, {'category': 'community', 'blog_count': '2'}, {'category': 'people', 'blog_count': '1'}]>
I have tried doing Blog.objects.values('category').order_by('category').distinct('category').count()
and got result as 3
which is true because it had count the total distinct values related to category. 我尝试做Blog.objects.values('category').order_by('category').distinct('category').count()
并得到结果为3
,这是正确的,因为它已经计算了与类别。
Django annotate count with a distinct field this post provide a solution where we can count fields based on two models. Django使用不同的字段注释计数,本文提供了一种解决方案,其中我们可以基于两个模型对字段进行计数。 But i want the results from the same model. 但是我想要来自同一模型的结果。
You can obtain such queryset with: 您可以通过以下方式获取此类查询集:
from django.db.models import Count
Blog.objects.values('category').annotate(
blog_count=Count('pk')
).order_by('category')
That being said, the modeling might not be optimal, since it creates a lot of data duplication . 话虽如此,建模可能不是最佳的,因为它会创建大量数据重复 。 Imagine if you later want to rename a category
, then this would result in a huge amount of work, since these categories can be spread over a lot of tables. 想象一下,如果您以后要重命名一个category
,那么这将导致大量的工作,因为这些类别可以分布在很多表上。
It makes more sense to then implement a Category
model, like: 然后实现Category
模型更有意义,例如:
class Category(models.Model):
name = models.CharField(max_length=255, unique=True)
class Blog(DateTimeModel):
title = models.CharField(max_length=255)
description = models.TextField()
category = models.ForeignKey(Category, null=True)
Then you can annotate the Category
objects, like: 然后,您可以注释Category
对象,例如:
from django.db.models import Count
Category.objects.annotate(
blog_count=Count('blog')
)
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