作业截止时间消息通知：

1、时间区段设置为24小时
2、只进行一次消息提醒

lib/tasks/homework_endtime.rake

@@ -4,11 +4,13 @@ namespace :homework_endtime do
   desc "send a message for Job deadline"
   task :message => :environment do
     current_day = Date.today.day
-    homework_commons = HomeworkCommon.where("end_time >?",Date.today)
+    homework_commons = HomeworkCommon.where("end_time >=?",Date.today)
     homework_commons.each do |homework_common|
-      if homework_common.end_time.day - Date.today.day < 2 && homework_common.end_time.year == Date.today.year
-        homework_common.course.student.each do |s|
-          homework_common.course_messages << CourseMessage.new(:user_id => s.student_id, :course_id => homework_common.course_id, :viewed => false, :status => true)
+      if CourseMessage.where("course_message_type =? and course_message_id =? and status =?", "HomeworkCommon", homework_common.id, 1).first.nil?
+        if homework_common.end_time.day - Date.today.day < 2 && homework_common.end_time.year == Date.today.year
+          homework_common.course.student.each do |s|
+            homework_common.course_messages << CourseMessage.new(:user_id => s.student_id, :course_id => homework_common.course_id, :viewed => false, :status => true)
+          end
         end
       end
     end