修复先删除课程下的某班级，再删除该课程报错

app/controllers/student_work_controller.rb

@@ -381,6 +381,7 @@ class StudentWorkController < ApplicationController
     @is_evaluation = @homework.homework_detail_manual && @homework.homework_detail_manual.comment_status == 2 && !@is_teacher #是不是匿评
     @show_all = false
 
+    # 0表示没有分组的学生，-1表示所有分组的学生
     if @group
       if @group == "0"
         none_group_students = @course.members.select{ |member| member.course_group_id == 0 }

app/controllers/syllabuses_controller.rb

@@ -88,7 +88,7 @@ class SyllabusesController < ApplicationController
   end
 
   def destroy
-    if @syllabus && @syllabus.courses.empty?
+    if @syllabus && @syllabus.courses.not_deleted.empty?
       @syllabus.destroy
       redirect_to user_courselist_user_path(User.current.id)
     end

app/views/syllabuses/_delete_syllabus.html.erb

@@ -1,6 +1,6 @@
 <br>
 <div style='width:470px;text-align:center;font-family: "微软雅黑","宋体"' class="f14">
-  <% if @syllabus.courses.empty? || @syllabus.courses.not_deleted.empty? %>
+  <% if @syllabus.courses.not_deleted.empty? %>
     确认删除该课程吗？
   <% else %>
     该课程下已经存在班级，不能删除。
@@ -8,7 +8,7 @@
 </div>
 </br>
 <div style='width:164px; margin:0 auto; text-align:center; font-family: "微软雅黑","宋体"'>
-  <% if @syllabus.courses.empty?|| @syllabus.courses.not_deleted.empty? %>
+  <% if @syllabus.courses.not_deleted.empty? %>
       <%=link_to '确认', syllabus_path(@syllabus), :class => 'Blue-btn fl', :method => 'delete'%>
       <a href='javascript:void(0);' class='Blue-btn fl' onclick='hideModal()'>关闭</a>
   <% else %>