_form.rb

= f.select :path, Page.all.collect {|p|[p.url_link_name, p.slug  ]  } << ["blogs", "/blogs"] << ["none", "#"] << ["home", "/"]

page.rb

class Page < ActiveRecord::Base
  mount_uploader :image, PageLeftImageUploader
  has_many :subcategories, -> { order(position: :asc)}
  extend FriendlyId
  friendly_id :url_link_name, use: :slugged
  acts_as_list scope: :nav_menu
  default_scope { order(position: :asc) }
end

subcategory.rb

class Subcategory < ActiveRecord::Base
  mount_uploader :image, LeftImageUploader
  belongs_to :page
  extend FriendlyId
  friendly_id :url_link_name, use: :slugged
  acts_as_list scope: :page

  def parent_id
    self.page_id
  end

  def position_count
    Subcategory.where("position IS NOT NULL").where("page_id = ?", self.page_id).count
  end

  def self.active_links
    Subcategory.where("position IS NOT NULL")
  end

  def hierarchy_list
    "#{self.page.url_link_name} > #{self.url_link_name}"
  end
end