减少sql查询， logger ===> Rails.logger

app/helpers/courses_helper.rb

@@ -150,7 +150,7 @@ module CoursesHelper
   #当前用户是不是指定课程的学生
   def is_cur_course_student? course
     people = []
-    course.members.each do |member|
+    course.members.includes(:roles, :user).each do |member|
       if StudentRoles.include? member.roles.first.id
         people <<  member.user
       end

app/models/mailer.rb

@@ -51,7 +51,7 @@ class Mailer < ActionMailer::Base
              when :User
                user_newfeedback_user_url(journals_for_message.jour, anchor: "word_li_#{journals_for_message.id}")
              else
-               logger.error "[Builds a Mail::Message ERROR] journalsForMessage's jour is unkown type, journalsForMessage.id = #{journals_for_message.id}"
+               Rails.logger.error "[Builds a Mail::Message ERROR] journalsForMessage's jour is unkown type, journalsForMessage.id = #{journals_for_message.id}"
                return -1
            end
     #如果是直接留言并且留言对象是Project并且Project类型是课程