class AddPositionForInforms < ActiveRecord::Migration[5.2]
  def change
    add_column :informs, :position, :integer, :default => 1

    course_ids = Inform.where(container_type: 'Course').pluck(:container_id).uniq
    courses = Course.where(id: course_ids)

    courses.find_each do |course|
      next if course.informs.count == 1
      informs = course.informs.order("created_at asc")
      informs.each_with_index do |inform, index|
        inform.update_attribute(:position, index+1)
      end
    end

  end
end