Django ORM用作表达式的子查询返回的多行

from django.db import models

class Author(models.Model):
    name = models.CharField(max_length=100)

class Book(models.Model):
    title = models.CharField(max_length=100)
    author = models.ForeignKey(Author, on_delete=models.CASCADE)

from django.db.models import Count, Subquery, OuterRef

# 首先，我们创建一个子查询，计算每个作者的书的数量
book_count_subquery = Book.objects.filter(author=OuterRef('pk')).values('author').annotate(count=Count('id'))

# 然后，我们将子查询添加到Author模型中，并选择我们感兴趣的字段
authors_with_book_count = Author.objects.annotate(book_count=Subquery(book_count_subquery.values('count')[:1]))

# 最后，我们可以遍历结果并打印每个作者及其书的数量
for author in authors_with_book_count:
    print(f"{author.name}: {author.book_count}")