Fix MilestonesFinder to pass relations to scope

Instead of querying relations into ids we just pass them to the model
scope because the scope supports it now.

Also changes other calls to `Milestone.for_projects_and_groups`

app/controllers/projects/milestones_controller.rb

@@ -144,7 +144,7 @@ class Projects::MilestonesController < Projects::ApplicationController
   def search_params
     if request.format.json? && project_group && can?(current_user, :read_group, project_group)
-      groups = project_group.self_and_ancestors_ids
+      groups = project_group.self_and_ancestors.select(:id)
     end
     params.permit(:state).merge(project_ids: @project.id, group_ids: groups)

app/finders/milestones_finder.rb

@@ -3,8 +3,8 @@
 # Search for milestones
 #
 # params - Hash
-#   project_ids: Array of project ids or single project id.
-#   group_ids: Array of group ids or single group id.
+#   project_ids: Array of project ids or single project id or ActiveRecord relation.
+#   group_ids: Array of group ids or single group id or ActiveRecord relation.
 #   order - Orders by field default due date asc.
 #   title - filter by title.
 #   state - filters by state.
@@ -12,17 +12,13 @@
 class MilestonesFinder
   include FinderMethods
-  attr_reader :params, :project_ids, :group_ids
+  attr_reader :params
   def initialize(params = {})
-    @project_ids = Array(params[:project_ids])
-    @group_ids = Array(params[:group_ids])
     @params = params
   end
   def execute
-    return Milestone.none if project_ids.empty? && group_ids.empty?
-
     items = Milestone.all
     items = by_groups_and_projects(items)
     items = by_title(items)
@@ -34,7 +30,7 @@ class MilestonesFinder
   private
   def by_groups_and_projects(items)
-    items.for_projects_and_groups(project_ids, group_ids)
+    items.for_projects_and_groups(params[:project_ids], params[:group_ids])
   end
   # rubocop: disable CodeReuse/ActiveRecord

app/models/milestone.rb

@@ -45,7 +45,7 @@ class Milestone < ActiveRecord::Base
     groups = groups.compact if groups.is_a? Array
     groups = [] if groups.nil?
-    where(project: projects).or(where(group: groups))
+    where(project_id: projects).or(where(group_id: groups))
   end
   scope :order_by_name_asc, -> { order(Arel::Nodes::Ascending.new(arel_table[:title].lower)) }
@@ -191,7 +191,7 @@ class Milestone < ActiveRecord::Base
     return STATE_COUNT_HASH unless projects || groups
     counts = Milestone
-               .for_projects_and_groups(projects&.map(&:id), groups&.map(&:id))
+               .for_projects_and_groups(projects, groups)
                .reorder(nil)
                .group(:state)
                .count
@@ -275,8 +275,7 @@ class Milestone < ActiveRecord::Base
     if project
       relation = Milestone.for_projects_and_groups([project_id], [project.group&.id])
     elsif group
-      project_ids = group.projects.map(&:id)
-      relation = Milestone.for_projects_and_groups(project_ids, [group.id])
+      relation = Milestone.for_projects_and_groups(group.projects.select(:id), [group.id])
     end
     title_exists = relation.find_by_title(title)

app/services/issuable_base_service.rb

@@ -61,10 +61,10 @@ class IssuableBaseService < BaseService
     return unless milestone_id
     params[:milestone_id] = '' if milestone_id == IssuableFinder::NONE
-    group_ids = project.group&.self_and_ancestors&.pluck(:id)
+    groups = project.group&.self_and_ancestors&.select(:id)
     milestone =
-      Milestone.for_projects_and_groups([project.id], group_ids).find_by_id(milestone_id)
+      Milestone.for_projects_and_groups([project.id], groups).find_by_id(milestone_id)
     params[:milestone_id] = '' unless milestone
   end

app/services/milestones/promote_service.rb

@@ -82,11 +82,9 @@ module Milestones
     end
     # rubocop: enable CodeReuse/ActiveRecord
-    # rubocop: disable CodeReuse/ActiveRecord
     def group_project_ids
-      @group_project_ids ||= group.projects.pluck(:id)
+      group.projects.select(:id)
     end
-    # rubocop: enable CodeReuse/ActiveRecord
     def raise_error(message)
       raise PromoteMilestoneError, "Promotion failed - #{message}"

app/services/projects/autocomplete_service.rb

@@ -14,7 +14,7 @@ module Projects
         order: { due_date: :asc, title: :asc }
       }
-      finder_params[:group_ids] = @project.group.self_and_ancestors_ids if @project.group
+      finder_params[:group_ids] = @project.group.self_and_ancestors.select(:id) if @project.group
       MilestonesFinder.new(finder_params).execute.select([:iid, :title])
     end

changelogs/unreleased/47988-improve-milestone-queries-with-subqueries.yml

+---
+title: Improve milestone queries using subqueries instead of separate queries for ids
+merge_request: 24325
+author:
+type: performance

lib/banzai/filter/milestone_reference_filter.rb

@@ -101,9 +101,9 @@ module Banzai
       def self_and_ancestors_ids(parent)
         if group_context?(parent)
-          parent.self_and_ancestors_ids
+          parent.self_and_ancestors.select(:id)
         elsif project_context?(parent)
-          parent.group&.self_and_ancestors_ids
+          parent.group&.self_and_ancestors&.select(:id)
         end
       end

spec/models/milestone_spec.rb

@@ -286,8 +286,8 @@ describe Milestone do
     end
     context 'relations as params' do
-      let(:projects) { Project.where(id: project.id) }
-      let(:groups) { Group.where(id: group.id) }
+      let(:projects) { Project.where(id: project.id).select(:id) }
+      let(:groups) { Group.where(id: group.id).select(:id) }
       it_behaves_like 'filters by projects and groups'
     end