如何使模型中的函数像字段一样起作用？

Question

I have a Post model that links wth PostScore through ForeignKey:

class Post(models.Model):
user = models.ForeignKey(User, blank=True, null=True)
title = models.TextField(max_length=76)
...


class PostScore(models.Model):
    user = models.ForeignKey(User, blank=True, null=True)
    post = models.ForeignKey(Post, related_name='score')
    upvotes = models.IntegerField(default=0)
    downvotes = models.IntegerField(default=0)

    def trending(self):
        score = self.upvotes - self.downvotes
        return score

So when I try to sort my Posts like this:

posts = Post.objects.all().order_by('-score__upvotes')

It works fine but how would I be able to sort by trending ?:

posts = Post.objects.all().order_by('-score__trending')

the above code creates this error:

FieldError at /news/
Cannot resolve keyword 'trending' into field. Choices are: downvotes, id, post, post_id, upvotes, user, user_id

Answer 1

使用注释方法计算得分差异，然后使用该计算字段排序。

Post.objects.annotate(score_diff=F('upvotes') - F('downvotes')).order_by('-score_diff')