如何计算一组答案？一次查询得分？

Question

我正在编写一个类似于 Stackoverflow 的网络应用程序。我如何查询问题并用其分数注释每个问题，这只是它的赞成票数减去它的反对票数。

class Question(models.Model):
    pass

class Answer(models.Model):
    pass

VOTE_CHOICES = (
    ('U', 'Up'),
    ('D', 'Down'),
)

class Vote(models.Model):
    user = models.ForeignKey(User)
    answer = models.ForeignKey(Answer)
    type = models.CharField(max_length=1, choices=VOTE_CHOICES, db_index=True) 

    class Meta:
        unique_together = (("user", "answer"),)

Answer 1

VOTE_CHOICES = (
    (1, 'Up'),
    (-1, 'Down'),
)

会让事情变得更容易：

# q - your question
Vote.objects.filter(answer__question=q).aggregate(Sum('type'))

# all questions annotated
Vote.objects.values('answer__question_id').annotate(score=Sum('type')).order_by()

Answer 2

虽然DrTyrsa的回答是100%正确的。如果确实需要 VOTE_CHOICES 为“U”和“D”，您可以使用以下内容。

votes = Vote.objects.filter(answer__question=q)
rank = votes.filter(type='U').count() - votes.filter(type='D').count()