teachers_count = 0
json.data do
  json.array! @activities do |d|
    json.id d.id
    json.name d.name
    json.days d.days
    json.teachers_count d.activity_teachers_count
    teachers_count += d.activity_teachers_count
    json.return_rate d.return_rate
    json.students_count d.students_count || 0
    json.course_rate d.course_rate
    json.start_at d.start_at ? d.start_at.to_s(:date) : ''
    json.clazz_id d.clazz_id
    json.staff d.staff&.user&.real_name
    json.staff_manage d.manages.map { |d| d.staff.user.real_name}.uniq.join("、")
    json.staff_assist d.assists.map { |d| d.staff.user.real_name}.uniq.join("、")
    json.expert d.experts.pluck(:name).join("、")
  end
end

json.totalRow do
  json.teachers_count teachers_count.to_s
end
json.code 0
json.count @activities.total_count