an concern

sluggable.rb

module Sluggable
  extend ActiveSupport::Concern

  included do
    before_create :set_slug
    validates :slug, uniqueness: { case_sensitive: false }

    scope :from_param, -> param { find_by(slug: param) }
  end

  def to_param() slug end

  private
    def set_slug
      number = 1
      begin
        slug = name.parameterize
        slug << "-#{number}" if number > 1
        number += 1
      end while self.class.where(slug: slug).exists?
    end
end