如何使用Django的ORM过滤包含多对多关系中的多个元素的所有对象？

Question

我在 Django 中有两个类通过 ManyToManyField 链接（User 类是内置的 User 模型）：

from django.contrib.auth.models import User

class Activity():
    participants = models.ManyToManyField(User, related_name='activity_participants')

我想找到两个用户同时参与的所有活动。

我设法使用原始查询解决了我的问题（我的应用名称是“core”，因此表名中的“core”前缀）：

SELECT ca.id FROM core_activity_participants AS cap, core_activity AS ca
INNER JOIN core_activity_participants AS cap2 ON cap.activity_id
WHERE cap.user_id == 1 AND cap2.user_id == 2
    AND cap.activity_id == cap2.activity_id
    AND ca.id == cap.activity_id

但是，如果可能的话，我想避免使用原始查询，因为它会破坏我应用其他部分的一致性。如何使用 Django 的 ORM 进行此查询或等效查询？

Answer 1

如果您使用的是 Django 1.11 或更高版本，intersection 查询集方法将为您提供所需的记录。

# u1 and u2 are User instances
u1_activities = Activity.objects.filter(participants=u1)
u2_activities = Activity.objects.filter(participants=u2)
common_activities = u1_activities.intersection(u2_activities)

会产生类似这样的查询：

SELECT "core_activity"."id"
FROM "core_activity"
INNER JOIN "core_activity_participants"
ON ("core_activity"."id" = "core_activity_participants"."activity_id")
WHERE "core_activity_participants"."user_id" = 1
INTERSECT
SELECT "core_activity"."id"
FROM "core_activity"
INNER JOIN "core_activity_participants"
ON ("core_activity"."id" = "core_activity_participants"."activity_id")
WHERE "core_activity_participants"."user_id" = 2

如果您想检查超过 2 个用户之间的活动重叠，您还可以向交集添加额外的查询集。

更新：

另一种适用于旧 Django 版本的方法是

u1_activities = u1.activity_participants.values_list('pk', flat=True)
common_activities = u2.activity_participants.filter(pk__in=u1_activities)

这会产生类似的查询

SELECT "core_activity"."id"
FROM "core_activity"
INNER JOIN "core_activity_participants"
ON ("core_activity"."id" = "core_activity_participants"."activity_id")
WHERE (
    "core_activity_participants"."user_id" = 2
    AND "core_activity"."id" IN (
        SELECT U0."id"
        FROM "core_activity" U0
        INNER JOIN "core_activity_participants" U1
        ON (U0."id" = U1."activity_id")
        WHERE U1."user_id" = 1
    )
)