portfolio.rb

class Portfolio
  require 'slug'
  include Mongoid::Document
  include Mongoid::Slug
  include ComparableByIndex
  include CanBePublished
  field :title, type: String
  slug :title, history: true
  field :description, type: String
  embeds_many :portfolio_items, cascade_callbacks: true
  validates_presence_of :title
  #Mongoid::Slug does not yet set these:
  index({'portfolio_items._slugs' => 1}, {unique: true})
  index({'portfolio_items.images._slugs' => 1}, {unique: true})

  before_save :apply_indices

  def get_item_index(item)
    return nil if item.nil?
    portfolio_items.published.sorted.entries.index { |x| x.id == item.id }
  end

  def next_item(item)
    index = get_item_index(item)
    return nil if index.nil?
    (index + 1) == portfolio_items.published.count ? nil : portfolio_items.published.sorted.entries[index + 1]
  end

  def previous_item(item)
    index = get_item_index(item)
    return nil if index.nil?
    index == 0 ? nil : portfolio_items.published.sorted[index - 1]
  end

  private
  def apply_indices
    new_items = portfolio_items.where(index: -1)
    count = portfolio_items.count
    new_items.each do |item|
      item.index = count
      count = count + 1
    end
  end

end