You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: discipline_lesson_plan_cloner_form.rb
    path of file: ./repos/i-diario/app/forms
    
    the code of the file until where you have to start completion: class DisciplineLessonPlanClonerForm < ApplicationRecord
  has_no_table

  attr_accessor :discipline_lesson_plan_id, :teacher, :entity_id

  valid
    
  def set_field(message)
    if message.start_with? I18n.t('activerecord.attributes.discipline_lesson_plan.lesson_plan.start_at')
      :start_at
    elsif message.start_with? I18n.t('activerecord.attributes.discipline_lesson_plan.lesson_plan.end_at')
      :end_at
    else
      :classroom_id
    end