查询中的 Django ORM 连接子表

Question

我想使用Django ORM。我构建 SQL 查询：

select itinerary.id, count(users.home_location_id) from itinerary_itinerary as itinerary left join (select to_applicationuser_id as id, users.home_location_id from custom_auth_applicationuser_friends as friends join custom_auth_applicationuser as users on friends.to_applicationuser_id = users.id where from_applicationuser_id = 28)
    as users on itinerary.location_id = users.home_location_id 
    WHERE user_id = 28 
    GROUP BY itinerary.id, users.home_location_id

谁能告诉我如何用子查询的表进行左连接？
28 是当前用户 ID。
我使用类似的东西：

Itinerary.object.filter(user_id=28).extra(
            tables=['(select to_applicationuser_id as id, users.home_location_id from custom_auth_applicationuser_friends as friends join custom_auth_applicationuser as users on friends.to_applicationuser_id = users.id where from_applicationuser_id = 28) as users'],
            where=['itinerary.location_id = users.home_location_id']
        )

但我得到了错误

ProgrammingError 关系"(选择to_applicationuser_id为id, users.home_location_id from" 不存在

UPD

模型（只是简单的方案）：

class ApplicationUser(models.Model):
    name = models.CharField(max_length=255)
    home_location = models.ForeignKey(Location)
    friends = models.ManyToManyFieled('self')

class Location(models.Model):
    loc_name = models.CharFiled(max_length=255)

class Itinerary(models.Model):
    user = models.ForeignKey(ApplicationUser)
    location = models.ForeignKey(Location)

Answer 1

当您添加额外的表时，它们会被添加到不接受 sql 语句的 from 列表中。 我认为您根本不需要在这里使用额外的东西，您可以使用 ORM 获得类似的查询，而无需加入 select 语句。以下代码使用过滤和注释，将给出与我能够理解您的查询一样多的结果：

ApplicationUser.objects.filter(
    Q(itinerary__location_id = F('friends__home_location_id')) |
    Q(friends__home_location__isnull=True),
    id=28,                                                    
    ).values_list(
        'itinerary__id', 'friends__home_location_id'
    ).annotate(location_count = Count('friends__home_location_id')
    ).values_list('itinerary__id', 'location_count')