Django-用ManytoMany关系计数来注释 [英] Django - Annotate with count across ManytoMany relationships

问题描述

我找不到用多对多关系中的元素使用次数计数来注释查询集的方法。

I am not able to find the way to annotate a queryset with a count of how many times an element is used in a many-to-many relationship.

class Profile(models.Model):
    [...]
    # Profile can have multiple roles
    roles = models.ManyToManyField('Role', blank=True)
    [...]

class Role(models.Model):
    company = models.ForeignKey(Company, on_delete=models.CASCADE)
    name = models.CharField(blank=True, max_length=30)
    description = models.CharField(blank=True, max_length=300)
    [...]   

例如，我将有5个角色：

For example I would have 5 roles:

• Role1


• Role2


• Role3


• Role4


• Role5

• Role1
• Role2
• Role3
• Role4
• Role5

和分配了以下角色的2个配置文件：

And 2 profiles with following roles assigned:

• 个人资料1
  
  
  
  
  • 角色1
  
  
  • 角色2
  
  
  
  
  • 角色e 1
  
  
  • 角色3
  
  
  • 角色4
  
  

  我想查询角色模型并注释具有该角色的配置文件数量。

  I want to query the Role model and annotate with the number of profile that have that role.

  因此返回一个查询集，例如

  So return a queryset like

  Role1: company, name, description, profile_count=2
  Role2: company, name, description, profile_count=1
  

  etc ...

  我已经尝试过了，但是不起作用：

  I have tried that but it does not work:

  Role.objects.annotate(profile_count=Count('profile__roles'))
  

  似乎返回

  是否知道可以在Django中本地完成还是需要原始SQL请求？

  Any idea if that can be done natively in Django or if a raw SQL request is necessary?

  谢谢！

  推荐答案

  如果我正确理解了您，则只需要这样：

  If i understand you correctly you just want this:

  Role.objects.annotate(profile_count=Count('profile'))
  

  几乎是您所写的。

  这篇关于Django-用ManytoMany关系计数来注释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！