Delete all users not in a specific group

Support
2

Answering my own question, having learned a few lessons.

  1. Yes, use UserDestroyer or your database will be littered with orphaned records.
  2. You might need to be clever about how you gather your unwanted users. I used this Data Explorer query to get a list of them, which I then bulk added them to a group called unwanted 
WITH included_users AS (
SELECT
gu.user_id
FROM group_users gu
JOIN groups g
ON g.id = gu.group_id
WHERE g.name = :included_group
),

excluded_users AS (
SELECT
gu.user_id
FROM group_users gu
JOIN groups g
ON g.id = gu.group_id
WHERE g.name = :excluded_group
)

SELECT 
     u.id AS user_id, u.username
FROM users as u
WHERE u.id in (SELECT user_id FROM included_users)
AND u.id NOT IN (SELECT user_id FROM excluded_users)
GROUP by u.id

How to destroy a lot of users:

Enter the Discourse app (./launcher enter app, etc) and run these:

rails c
 target_group = Group.find_by_name("unwanted")
 users = User.joins(:group_users).where(group_users:{group_id: target_group.id})
 users.each do |u|
  u.admin = false
  u.moderator = false
  u.save
  UserDestroyer.new(Discourse.system_user).destroy(u, delete_posts: true)
 end
Exit

It isn’t fast. For 6000 users it took 2 hours.

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