迁移报错问题

lib/tasks/statistic_subject_info.rake

@@ -47,8 +47,7 @@ namespace :subjects do
       subjects = subjects.where(id:ENV['subject_id'])
     end
     subjects.find_in_batches(batch_size: 20) do |s|
-      str = []
+      Parallel.each_with_index(s, in_processes: 4) do |subject, index, str = []|
-      Parallel.each(s, in_processes: 6) do |subject|
         puts("---------------------course_info_statistic: #{subject.id}")
         Rails.logger.info("---------------------course_info_statistic: #{subject.id}")
         data = Subjects::CourseUsedInfoService.call(subject)