Django聚合反向关系 [英] Django Aggregation Across Reverse Relationship

问题描述

给定这两个模型：

class Profile(models.Model):
    user = models.ForeignKey(User, unique=True, verbose_name=_('user'))
    about = models.TextField(_('about'), blank=True)
    zip = models.CharField(max_length=10, verbose_name='zip code', blank=True)
    website = models.URLField(_('website'), blank=True, verify_exists=False)

class ProfileView(models.Model):
    profile = models.ForeignKey(Profile)
    viewer = models.ForeignKey(User, blank=True, null=True)
    created = models.DateTimeField(auto_now_add=True)

我想获取所有配置文件按总体视图排序。我可以通过以下方式获取总体视图排列的配置文件列表：

I want to get all profiles sorted by total views. I can get a list of profile ids sorted by total views with:

ProfileView.objects.values('profile').annotate(Count('profile')).order_by('-profile__count')

但这只是一个字典的配置文件ID，这意味着我必须循环它，并将一组配置文件对象放在一起。哪些是其他许多查询，但仍然不会产生QuerySet。在这一点上，我也可以放弃原始的SQL。在我做之前，有没有办法从配置文件模型中做到这一点？ ProfileViews通过ForeignKey字段相关联，但并不像Profile模型所知道的那样，所以我不知道如何将两者绑在一起。

But that's just a dictionary of profile ids, which means I then have to loop over it and put together a list of profile objects. Which is a number of additional queries and still doesn't result in a QuerySet. At that point, I might as well drop to raw SQL. Before I do, is there a way to do this from the Profile model? ProfileViews are related via a ForeignKey field, but it's not as though the Profile model knows that, so I'm not sure how to tie the two together.

，我意识到我可以在Profile模型中存储视图作为属性，这可能是我在这里做的，但是我仍然有兴趣学习如何更好地使用聚合函数。

As an aside, I realize I could just store views as a property on the Profile model and that may turn out to be what I do here, but I'm still interested in learning how to better use the Aggregation functions.

推荐答案

ProfileViews是通过ForeignKey字段相关的，但它并不像Profile模型知道

ProfileViews are related via a ForeignKey field, but it's not as though the Profile model knows that

配置文件模型确实知道。
你应该可以这样做：

The Profile model actually does know that. You should be able to do something like:

  Profile.objects.all().annotate(count_views=Count('profileview__pk')).order_by('count_views')

修改 ：在这里，您可以找到关于跨越关系的查找的Django文档 http://docs.djangoproject.com/en/dev/topics/db/queries/#lookups-that-span-relationships

Edit: Here you can find Django docs about lookups that span relationships http://docs.djangoproject.com/en/dev/topics/db/queries/#lookups-that-span-relationships

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