Remove N + 1 for milestones issues

When API request performed for multiple milestone issues
the number of SQL requests depends on the number of issues

app/models/issue.rb

@@ -113,7 +113,6 @@ class Issue < ApplicationRecord
 
   scope :preload_associated_models, -> { preload(:assignees, :labels, project: :namespace) }
   scope :with_web_entity_associations, -> { preload(:author, :project) }
-  scope :with_api_entity_associations, -> { preload(:timelogs, :assignees, :author, :notes, :labels, project: [:route, { namespace: :route }] ) }
   scope :with_label_attributes, ->(label_attributes) { joins(:labels).where(labels: label_attributes) }
   scope :with_alert_management_alerts, -> { joins(:alert_management_alert) }
   scope :with_prometheus_alert_events, -> { joins(:issues_prometheus_alert_events) }

changelogs/unreleased/id-n-1-for-milestone-issues.yml

+---
+title: Remove N + 1 for milestones issues
+merge_request: 57349
+author:
+type: performance

lib/api/milestone_responses.rb

@@ -80,7 +80,7 @@ module API
 
           params = build_finder_params(milestone, parent)
 
-          issuables = finder_klass.new(current_user, params).execute
+          issuables = finder_klass.new(current_user, params).execute.with_api_entity_associations
           present paginate(issuables), with: entity, current_user: current_user
         end
 

spec/requests/api/group_milestones_spec.rb

@@ -64,6 +64,24 @@ RSpec.describe API::GroupMilestones do
     end
   end
 
+  describe 'GET /groups/:id/milestones/:milestone_id/issues' do
+    let!(:issue) { create(:issue, project: project, milestone: milestone) }
+
+    def perform_request
+      get api("/groups/#{group.id}/milestones/#{milestone.id}/issues", user)
+    end
+
+    it 'returns multiple issues without performing N + 1' do
+      perform_request
+
+      control_count = ActiveRecord::QueryRecorder.new { perform_request }.count
+
+      create(:issue, project: project, milestone: milestone)
+
+      expect { perform_request }.not_to exceed_query_limit(control_count)
+    end
+  end
+
   def setup_for_group
     context_group.update(visibility_level: Gitlab::VisibilityLevel::PUBLIC)
     context_group.add_developer(user)