osem-fcy/lib/tasks/several_schedules.rake

namespace :data do
  desc 'Move the start_time and room attributes from Event to EventSchedule'

  task move_events_attributes: :environment do
    Program.all.each do |program|
      schedule = Schedule.create(program: program)
      program.selected_schedule = schedule
      program.save
      program.events.each do |event|
        unless event.room_id.nil?
          # we can not use .room as this relation has been removed
          EventSchedule.create(event: event,
                               schedule: schedule,
                               room_id: event.room_id)
          event.room_id = nil
          event.save
        end
      end
    end
    puts 'The start_time and room attributes has been moved from Event to EventSchedule'
  end
end