按聚合字段值排序QuerySet [英] Order a QuerySet by aggregate field value

问题描述

假设我有以下模型：

  class Contest：
 title = models.CharField（max_length = 200）
 description = models.TextField（）
 
 class Image：
 title = models.CharField（max_length = 200）
 description = models.TextField b $ b contest = models.ForeignKey（Contest）
 user = models.ForeignKey（User）
 
 def score（self）：
 return self.vote_set.all （model.Sum（'value'））['value__sum'] 
 
 class Vote：
 value = models.SmallIntegerField（）
 user = models.ForeignKey 
 image = models.ForeignKey（Image）
  

网站的用户可以贡献他们的图片到几个比赛。然后其他用户可以投票或投票。
一切正常，但现在我想显示一个页面，用户可以看到所有的贡献的一个特定的比赛。图像应按他们的分数排序。
因此，我尝试以下：

  Contest.objects.get（pk = id）.image_set.order_by（'分数'）
  

因为我担心它不工作，因为'score'

当然，我忘记了Django中的新的聚合支持和它的注释功能。

所以查询可能如下所示：

  Contest.objects.get（pk = id）.image_set.annotate（score = Sum（'vote__value'））。order_by（'score'）
  pre> 
Let's say I have the following model:
class Contest:
    title = models.CharField( max_length = 200 )
    description = models.TextField()

class Image:
    title = models.CharField( max_length = 200 )
    description = models.TextField()
    contest = models.ForeignKey( Contest )
    user = models.ForeignKey( User )

    def score( self ):
        return self.vote_set.all().aggregate( models.Sum( 'value' ) )[ 'value__sum' ]

class Vote:
    value = models.SmallIntegerField()
    user = models.ForeignKey( User )
    image = models.ForeignKey( Image )
The users of a site can contribute their images to several contests. Then other users can vote them up or down.
Everything works fine, but now I want to display a page on which users can see all contributions to a certain contest. The images shall be ordered by their score.
Therefore I tried the following:
Contest.objects.get( pk = id ).image_set.order_by( 'score' )
As I feared it doesn't work since 'score' is no database field that could be used in queries.
解决方案
Oh, of course I forget about new aggregation support in Django and its annotate functionality.

So query may look like this:
Contest.objects.get(pk=id).image_set.annotate(score=Sum('vote__value')).order_by( 'score' )


                        
这篇关于按聚合字段值排序QuerySet的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！