教学案例的封面图片显示

app/helpers/application_helper.rb

@@ -4381,7 +4381,7 @@ module ApplicationHelper
       elsif  attachment.container_type == "Bid" && attachment.container && attachment.container.courses
         course = attachment.container.courses.first
         candown = User.current.member_of_course?(attachment.container.courses.first) || (course.is_public == 1 && attachment.is_public == 1)
-      elsif attachment.container_type == "Library" #教学案例允许下载
+      elsif attachment.container_type == "Library" || attachment.container.class.to_s == "Library" #教学案例允许下载
         candown = true
       elsif attachment.container_type == "ProjectPackage" #教学案例允许下载
         candown = true