Add OncallScheduleEntity to users in Admin helper

app/controllers/admin/users_controller.rb

@@ -13,7 +13,7 @@ class Admin::UsersController < Admin::ApplicationController
   def index
     @users = User.filter_items(params[:filter]).order_name_asc
     @users = @users.search_with_secondary_emails(params[:search_query]) if params[:search_query].present?
-    @users = @users.includes(:authorized_projects) # rubocop: disable CodeReuse/ActiveRecord
+    @users = users_with_included_associations(@users)
     @users = @users.sort_by_attribute(@sort = params[:sort])
     @users = @users.page(params[:page])
 
@@ -228,6 +228,10 @@ class Admin::UsersController < Admin::ApplicationController
 
   protected
 
+  def users_with_included_associations(users)
+    users.includes(:authorized_projects) # rubocop: disable CodeReuse/ActiveRecord
+  end
+
   def admin_making_changes_for_another_user?
     user != current_user
   end

app/serializers/admin/user_entity.rb

@@ -30,3 +30,5 @@ module Admin
     end
   end
 end
+
+Admin::UserEntity.prepend_if_ee('EE::Admin::UserEntity')

ee/app/controllers/ee/admin/users_controller.rb

@@ -19,6 +19,11 @@ module EE
 
       private
 
+      override :users_with_included_associations
+      def users_with_included_associations(users)
+        super.includes(:oncall_schedules) # rubocop: disable CodeReuse/ActiveRecord
+      end
+
       override :log_impersonation_event
       def log_impersonation_event
         super

ee/app/serializers/ee/admin/user_entity.rb

+# frozen_string_literal: true
+
+module EE
+  module Admin
+    module UserEntity
+      extend ActiveSupport::Concern
+
+      prepended do
+        expose :oncall_schedules, with: ::IncidentManagement::OncallScheduleEntity
+
+        def oncall_schedules
+          object.oncall_schedules.uniq
+        end
+      end
+    end
+  end
+end

ee/spec/serializers/ee/admin/user_entity_spec.rb

+# frozen_string_literal: true
+
+require "spec_helper"
+
+RSpec.describe Admin::UserEntity do
+  let_it_be(:user) { build_stubbed(:user) }
+
+  let(:request) { double('request') }
+
+  let(:entity) do
+    described_class.new(user, request: request)
+  end
+
+  describe '#as_json' do
+    subject { entity.as_json&.keys }
+
+    it 'exposes correct attributes' do
+      is_expected.to include(:oncall_schedules)
+    end
+  end
+end