django中筛选出的图书清单的每个作者的书数 [英] book count per author for filtered book list in django

问题描述

简短的问题。
我有两个模型：

Short question. I have two models:

class Author(models.Model):
    name = models.CharField(max_length=250)

class Book(models.Model):
    title = models.CharField(max_length=250)
    author = models.ManyToManyField(Author)

一个视图：

def filter_books(request):
    book_list = Book.objects.filter(...)

如何在模板的下一个内容中显示：

How can I display in template next content:

Authors in selected books:
    Author1: book_count
    Author2: book_count
    ...

推荐答案

让我们逐步构建查询。

首先，在 book_list 中找到拥有一本书的作者。

First, get the authors who have a book in book_list.

authors = Author.objects.filter(book__in=book_list)

诀窍是要认识到，对于 book_list 中的每本书，作者都会出现一次。然后，我们可以使用注释来计数作者出现的次数。

The trick is to realise that an author will appear once for each book in book_list. We can then use annotate to count the number of times the author appears.

# remember to import Count!
from django.db.models import Count

authors = Author.objects.filter(book__in=book_list
          ).annotate(num_books=Count('id')

在模板中，您可以执行以下操作：

In the template, you can then do:

Authors in selected books:
{% for author in authors %}
{{ author.name }}: {{ author.num_books }}<br />
{% endfor %}

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