Define last_pipeline in PipelineScheduleEntity

app/models/ci/pipeline_schedule.rb

@@ -44,10 +44,6 @@ module Ci
       self.next_run_at = Gitlab::Ci::CronParser.new(cron, cron_timezone).next_time_from(Time.now)
     end
 
-    def last_pipeline
-      self.pipelines&.last
-    end
-
     def schedule_next_run!
       save! # with set_next_run_at
     rescue ActiveRecord::RecordInvalid

lib/api/entities.rb

@@ -690,7 +690,9 @@ module API
       expose :id
       expose :description, :ref, :cron, :cron_timezone, :next_run_at, :active
       expose :created_at, :updated_at, :deleted_at
-      expose :last_pipeline, using: Entities::Pipeline
+      expose :last_pipeline, using: Entities::Pipeline do |pipeline_schedule|
+        pipeline_schedule.pipelines&.last
+      end
       expose :owner, using: Entities::UserBasic
     end