在Django ORM中，获取字段值在queryset中最大的记录

Consider a simple model:

考虑一个简单的模型:

class Person(models.Model):
    name = models.CharField(max_length=256)
    age = models.IntegerField()

I would like a single expression which returns a QuerySet of all of the Person objects whose age is maximal in the table. I.e. say there are 20 Person records, and the largest age is 70 but there are 3 distinct records which have that value. I would like my queryset to contain exactly those 3 Person objects.

我希望有一个表达式，它返回表中年龄最大的所有Person对象的QuerySet。也就是说，有20个人的记录，最大的年龄是70岁，但是有3个不同的记录有这个价值。我希望我的queryset恰好包含这3个Person对象。

I suppose I could do:

我想我可以:

Person.objects.filter(age=Person.objects.aggregate(models.Max('age'))['age__max'])

But wow that seems like a real mess. And it hits the database twice. Yuck.

但哇，这看起来真是一团糟。它会访问数据库两次。讨厌的东西。

Better alternatives?

其它更好的选择吗?

1 个解决方案

#1

I can't directly answer your question, but I feel like you shouldn't beat up for getting this in one query, making your code clear is also important. So why don't you do:

我不能直接回答您的问题，但是我觉得您不应该因为在一个查询中获得这个而感到紧张，使您的代码清晰也是很重要的。所以你为什么不这样做呢:

from django.db.models import Max
# assumes that you have at least one record
max_age = Person.objects.aggregate(Max('age'))['age__max']
oldest_folks = Person.objects.filter(age=max_age)

Max would do MAX in sql statement, filter would do a simple sql lookup, none of the operations are awfully expensive.

Max会做Max in sql语句，filter会做一个简单的sql查找，所有的操作都不会太贵。

#1