Django用聚合平均值注释

Question

在以下来自 django 文档的示例中，如何获取

Publisher.objects.all()

注释字段 average_rating 使用书籍评分的平均值计算，max_rating 使用书籍的最高评分计算？

from django.db import models

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

class Publisher(models.Model):
    name = models.CharField(max_length=300)
    num_awards = models.IntegerField()

class Book(models.Model):
    name = models.CharField(max_length=300)
    pages = models.IntegerField()
    price = models.DecimalField(max_digits=10, decimal_places=2)
    rating = models.FloatField()
    authors = models.ManyToManyField(Author)
    publisher = models.ForeignKey(Publisher)
    pubdate = models.DateField()

class Store(models.Model):
    name = models.CharField(max_length=300)
    books = models.ManyToManyField(Book)
    registered_users = models.PositiveIntegerField()

确切地说，我应该能够在查询集之后打印这样的内容：

for p in Publisher.objects.all().annotate(...):
    print p, p.average_rating, p.max_rating

Answer 1

您可以像这样使用book__rating 访问出版商的书籍：

Publisher.objects.annotate(average_rating=Avg('book__rating'), max_rating=Max('book__rating'))