page_tree_builder.rb

# Example usage within Gluttonberg
# Page.localized_tree("australia_english", :depth => (0..1))

def self.localized_tree(locale_name, page_opts = {})
  # Find all matching pages
  pages = Page.all({:order => [:position.asc]}.merge!(page_opts))
  if pages.empty?
    pages
  else
    # Find the localizations that belong to the pages passed in. This is done 
    # by collecting the page ids and using an IN condition in the query.
    page_ids = pages.collect {|p| p.id}
    l_opts = {:page_id => page_ids, :locale_name => locale_name}
    localizations = PageLocalization.all(l_opts).inject({}) do |memo, localization|
      memo[localization.page_id] = localization
      memo
    end
    # Sort everything ready to build a tree, and set the current localization 
    # for each.
    children  = Hash.new {|h, k| h[k] = []}
    top_level = []
    pages.each do |page|
      # Sort them into top level and child pages
      if page.parent_id
        children[page.parent_id] << page
      else
        top_level << page
      end
      # Associate the localization
      page.current_localization = localizations[page.id]
    end
    # Now to start off the recursive method which sorts the pages into a tree
    sort_pages([], top_level, children)
  end
end

private

Node = Stuct.new(:page, :children)

def sort_pages(collection, pages, children)
  pages.inject(collection) do |memo, page|
    memo << Node.new(page, sort_pages([], children.delete(page.id), children))
  end
end

# Example usage
# for node in pages
#   puts node.page.name
# end

set_depth.rb

property :depth, Integer, :writer => :private

before :save, :set_depth

def set_depth
  if attribute_dirty?(:parent_id)
    new_depth = (parent_id ? parent.depth + 1 : 0)
    attribute_set(:depth, new_depth)
  end
end