Fix N+1 queries for milestone search

app/models/milestone.rb

@@ -89,6 +89,10 @@ class Milestone < ApplicationRecord
       .order(:project_id, :group_id, :due_date).select('DISTINCT ON (project_id, group_id) id')
   end
 
+  def self.with_web_entity_associations
+    preload(:group, project: [:project_feature, group: [:parent], namespace: :route])
+  end
+
   def participants
     User.joins(assigned_issues: :milestone).where("milestones.id = ?", id).distinct
   end

app/presenters/search_service_presenter.rb

@@ -10,7 +10,8 @@ class SearchServicePresenter < Gitlab::View::Presenter::Delegated
     issues: :with_web_entity_associations,
     merge_requests: :with_web_entity_associations,
     epics: :with_web_entity_associations,
-    notes: :with_web_entity_associations
+    notes: :with_web_entity_associations,
+    milestones: :with_web_entity_associations
   }.freeze
 
   SORT_ENABLED_SCOPES = %w(issues merge_requests).freeze

changelogs/unreleased/227383-fix-search-n-plus-1.yml

+---
+title: Fix N+1 for searching milestone scope
+merge_request: 57715
+author:
+type: performance

ee/app/models/ee/milestone.rb

@@ -10,6 +10,15 @@ module EE
       has_many :boards
     end
 
+    class_methods do
+      extend ::Gitlab::Utils::Override
+
+      override :with_web_entity_associations
+      def with_web_entity_associations
+        super.preload(project: [group: [:saml_provider]])
+      end
+    end
+
     def supports_milestone_charts?
       resource_parent&.feature_available?(:milestone_charts) && weight_available?
     end

ee/spec/features/search/elastic/global_search_spec.rb

@@ -78,9 +78,7 @@ RSpec.describe 'Global elastic search', :elastic, :sidekiq_inline do
       let(:object) { :milestone }
       let(:creation_args) { { project: project } }
       let(:path) { search_path(search: '*', scope: 'milestones') }
-      # N+1 queries still exist and will be fixed per
-      # https://gitlab.com/gitlab-org/gitlab/-/issues/325887
-      let(:query_count_multiplier) { 1 }
+      let(:query_count_multiplier) { 0 }
 
       it_behaves_like 'an efficient database result'
     end