分组作业和普通作业列表的排序

app/controllers/homework_commons_controller.rb

@@ -82,7 +82,9 @@ class HomeworkCommonsController < ApplicationController
     end
     @task_count = @homework_commons.size
 
-    @homework_commons = @homework_commons.order("position DESC").page(page).per(15)
+    order_str = @homework_type == 4 ? "position DESC" : "IF(ISNULL(homework_commons.publish_time),0,1), homework_commons.publish_time DESC,
+                                                  homework_commons.created_at DESC"
+    @homework_commons = @homework_commons.order(order_str).page(page).per(15)
 
     if @homework_type == 4
       @homework_commons = @homework_commons.includes(:homework_detail_manual, :published_settings, :shixuns)