Question

这是我失败的代码：

dashboard = Dashboard.objects.get(slug=slug)
users = User.objects.all() # list of users

for editor in dashboard.dashboardeditor_set.iterator:
    users.remove(editor.user)

错误： 'instancemethod'对象不可迭代

来自models.py：

class DashboardEditor(models.Model):
    dashboard = models.ForeignKey(Dashboard)
    user = models.ForeignKey(User)

有人可以帮我弄清楚如何从所有用户列表中清除编辑器吗？

谢谢！：）

Answer 1

我从错误消息中猜到你缺少括号：

 for editor in dashboard.dashboardeditor_set.iterator():

这是因为错误消息似乎暗示iterator在实例方法中，所以你需要调用它来获取实际的迭代器。

Answer 2

使用values_list()和exclude()的组合在单个查询中获取结果（使用嵌套的SELECT）：

dash = Dashboard.objects.get(slug=slug)
User.objects.exclude(id__in=dash.dashboardeditor_set.values_list('user', flat=True))

生成以下SQL：

SELECT "auth_user"."id",
       "auth_user"."username",
       "auth_user"."first_name",
       "auth_user"."last_name",
       "auth_user"."email",
       "auth_user"."password",
       "auth_user"."is_staff",
       "auth_user"."is_active",
       "auth_user"."is_superuser",
       "auth_user"."last_login",
       "auth_user"."date_joined"
FROM "auth_user"
WHERE NOT ("auth_user"."id" IN
             (SELECT U0."user_id"
              FROM "dashboard_dashboardeditor" U0
              WHERE U0."dashboard_id" = 1)) LIMIT 21  [0.68ms]

使用iterator会触发大约N + 2个查询，其中N是给定DashboardEditor的{{1}}个数：

Dashboard

此示例中有两个In [24]: users = list(User.objects.all()) SELECT "auth_user"."id", "auth_user"."username", "auth_user"."first_name", "auth_user"."last_name", "auth_user"."email", "auth_user"."password", "auth_user"."is_staff", "auth_user"."is_active", "auth_user"."is_superuser", "auth_user"."last_login", "auth_user"."date_joined" FROM "auth_user" [0.40ms] In [25]: for editor in dash.dashboardeditor_set.iterator(): ....: users.remove(editor.user) ....: SELECT "dashboard_dashboardeditor"."id", "dashboard_dashboardeditor"."user_id", "dashboard_dashboardeditor"."dashboard_id" FROM "dashboard_dashboardeditor" WHERE "dashboard_dashboardeditor"."dashboard_id" = 1 [0.15ms] SELECT "auth_user"."id", "auth_user"."username", "auth_user"."first_name", "auth_user"."last_name", "auth_user"."email", "auth_user"."password", "auth_user"."is_staff", "auth_user"."is_active", "auth_user"."is_superuser", "auth_user"."last_login", "auth_user"."date_joined" FROM "auth_user" WHERE "auth_user"."id" = 2 [0.25ms] SELECT "auth_user"."id", "auth_user"."username", "auth_user"."first_name", "auth_user"."last_name", "auth_user"."email", "auth_user"."password", "auth_user"."is_staff", "auth_user"."is_active", "auth_user"."is_superuser", "auth_user"."last_login", "auth_user"."date_joined" FROM "auth_user" WHERE "auth_user"."id" = 3 [0.24ms]，ORM运行了4个查询以获取非编辑用户的结果列表。

Django：如何“清理”用户列表

2 个答案: