diff --git a/lib/tasks/public_course.rake b/lib/tasks/public_course.rake
index 67d5603ab..ff50a4e28 100644
--- a/lib/tasks/public_course.rake
+++ b/lib/tasks/public_course.rake
@@ -68,12 +68,15 @@ namespace :public_course do
     case type.to_i
     when 1
       # 讨论区
-      created_on = random_time start_time, end_time
-      puts created_on
       messages = Message.where(board_id: course.boards)
       messages.each do |message|
+        created_on = random_time start_time, end_time
+        puts created_on
         message.update_columns(created_on: created_on, updated_on: created_on)
-        MessageDetail.where(message_id: message.id).update_all(created_at: created_on, updated_at: created_on)
+        MessageDetail.where(message_id: message.id).each do |detail|
+          rand_created_on = random_time start_time, end_time
+          detail.update_columns(created_at: rand_created_on, updated_at: rand_created_on)
+        end
       end
     when 2
       # 作业