json.courses @courses do |course|
  json.(course, :id, :name, :is_end, :evaluating_count)
  json.teachers course.teacher_users.map(&:real_name).join('、')
  json.student_count @student_count.fetch(course.id, 0)
  json.shixun_work_count @shixun_work_count.fetch(course.id, 0)
  json.attachment_count @attachment_count.fetch(course.id, 0)
  json.message_count @message_count.fetch(course.id, 0)
  json.other_work_count @exercise_count.fetch(course.id, 0) + @poll_count.fetch(course.id, 0) + @other_work_count.fetch(course.id, 0)
  json.activity_time @active_time[course.id]&.strftime('%Y-%m-%d %H:%M')
end
json.course_count @course_count