Optimize hosts controller query: use pluck instead of map for hostgroup_ids

[raman1236]

Description

Optimize database query in hosts controller to reduce unnecessary memory allocation.

Change

app/controllers/hosts_controller.rb - Use pluck instead of map

# Before
@hosts.map(&:hostgroup_id).compact.uniq

# After
@hosts.pluck(:hostgroup_id).compact.uniq

map(&:hostgroup_id) loads all Host ActiveRecord objects into memory and extracts the attribute in Ruby. pluck(:hostgroup_id) generates a SELECT hostgroup_id FROM ... query that returns only the needed column values directly from the database, avoiding unnecessary object instantiation. This is particularly impactful on the hosts index page which can display many hosts.

Note on previous user.rb change

The original PR also included a .where().any? → .exists?() change in user.rb. As correctly pointed out by @adamruzicka, Rails already optimizes .any? to generate the same efficient SELECT 1 AS one ... LIMIT 1 query, so that change was reverted.

[ofedoren]

Thanks, @raman1236, it'll need a ticket (https://projects.theforeman.org/projects/foreman/issues/new) and then updated commit message with the ticket's number. Otherwise LGTM.

[adamruzicka]

where(:id => id).any? generates SELECT "auth_sources".* FROM "auth_sources" WHERE ... and loads matching records into memory before checking presence. exists?(id) generates SELECT 1 AS one FROM "auth_sources" WHERE ... LIMIT 1 which is more efficient as it stops after finding one match and doesn't instantiate ActiveRecord objects. This runs on every user update validation.

Does it though?

> AuthSourceHidden.where(:id => 4).any?
2026-04-08T11:01:12 [D|sql|]   AuthSourceHidden Exists? (1.7ms)  SELECT 1 AS one FROM "auth_sources" WHERE "auth_sources"."type" = $1 AND "auth_sources"."id" = $2 LIMIT $3  [["type", "AuthSourceHidden"], ["id", 4], ["LIMIT", 1]]

> AuthSourceHidden.exists?(4)
2026-04-08T11:01:01 [D|sql|]   AuthSourceHidden Exists? (4.7ms)  SELECT 1 AS one FROM "auth_sources" WHERE "auth_sources"."type" = $1 AND "auth_sources"."id" = $2 LIMIT $3  [["type", "AuthSourceHidden"], ["id", 4], ["LIMIT", 1]]

[raman1236]

@adamruzicka Great catch — you're absolutely right! I tested this myself and confirmed that Rails' .any? already generates the optimized SELECT 1 AS one ... LIMIT 1 query, making it equivalent to .exists? at the SQL level.\n\nI've reverted the user.rb change and updated the PR to focus solely on the pluck vs map optimization in hosts_controller.rb, which does produce a genuinely different (more efficient) query by selecting only the hostgroup_id column instead of loading full ActiveRecord objects.

[raman1236]

Friendly ping — review feedback has been addressed (reverted the user.rb change, kept only the pluck optimization). The PR now focuses on a single targeted optimization in the hosts controller. Would appreciate another look. Thanks!

[stejskalleos]

@adamruzicka Great catch — you're absolutely right!

LOL.

[stejskalleos]

@raman1236, please squash the commits into one and change the commit message to Fixes #xxx Optimize hosts ... where the #xxx is the ID of the issue in our tracker, thank you.