Get Users with params and without others - sql

Question

I'm trying to get group's users with specific ids that are not admin.
For the moment I have:
group.users
.joins(:roles)
.where(id: user_ids)
.where.not(roles: { role_type: Role::Type::ADMIN })
.pluck(:id)
In my log I have:
SQL to load the group:
(0.3ms) SELECT "users"."id" FROM "users" INNER JOIN "groups_users"
ON "users"."id" = "groups_users"."user_id"
WHERE "groups_users"."group_id" = $1 [["group_id", 137375]]
SQL for the query above:
(0.6ms) SELECT "users"."id" FROM "users" INNER JOIN "roles"
ON "roles"."user_id" = "users"."id" AND "roles"."is_destroyed" = $1
INNER JOIN "groups_users" ON "users"."id" = "groups_users"."user_id"
WHERE "groups_users"."group_id" = $2 AND "users"."id" IN (82884, 82885)
AND "roles"."role_type" != $3 [["is_destroyed", "f"],
["group_id", 137375], ["role_type", 1]]
The problem is I always get all the users of the group with matching user_ids. The where.not is not effective.
I had to do something like
users_in_group = group.users.where(id: user_ids).pluck(:id)
users_in_group -= group.users.joins(:roles).where
(roles: { role_type: Role::Type::ADMIN}).pluck(:id)
I don't understand why.

Answer 1

If you want to exclude Admins even if they have other roles, you might use SQL EXISTS:
group.users
.where(id: user_ids)
.where("NOT EXISTS (SELECT 1 FROM roles WHERE user_id = users.id AND role_type = ?", Role::Type::ADMIN)
.pluck(:id)
And, handling typical objection to such advice: it's perfectly fine to get your hands dirty by writing fragments of SQL when you are using ActiveRecord in Rails. You shouldn't limit yourself to the (not so broad) possibilities of its DSL.
UPD.
To simplify your code, you can use Where Exists gem (disclosure: I've written it recently).
Add gem 'where_exists' to your Gemfile, run bundle install, and then the following should work:
group.users
.where(id: user_ids)
.where_not_exists(:roles, role_type: Role::Type::ADMIN)
.pluck(:id)