Generate a CSV from a collection action.

active_admin_generate_csv_collection_action.rb

collection_action :download_report, method: :get do
  users = User.where('created_at >= ?', Date.today - 1.month)
    csv = CSV.generate( encoding: 'Windows-1251' ) do |csv|
    # add headers
    csv << [ #Some header ]
    # add data
    users.each do |user|
      csv << [ user.created_at ]
    end      
  end
  # send file to user
  send_data csv.encode('Windows-1251'), type: 'text/csv; charset=windows-1251; header=present', disposition: "attachment; filename=report.csv"
end

action_item only: :index do
  link_to "csv report", download_report_admin_#{models}_path, method: :get
end 

index download_links: false do
  # off standard download link
end