如何在activeadmin中的索引上添加排序到自定义列？

I have these associations:

我有这些联想：

class Event < ApplicationRecord
  has_many :users_events
  has_many :users, through: :users_events
end

class UsersEvent < ApplicationRecord
  belongs_to :user
  belongs_to :event
end

class User < ApplicationRecord
  has_many :users_events
  has_many :events, through: :users_events
end
class Ev