tree_options_from_collection_for_select.rb

module ApplicationHelper
  def tree_options_from_collection_for_select(objects, value = :id, name = :name, selected = nil, options = {})
    options[:indent_with] ||= '- '
    options[:level] ||= 0
    
    objects.inject([]) do |entries, object|
      entries << [options[:indent_with] * options[:level] + object.send(name), object.send(value)]
      entries += tree_options_from_collection_for_select(object.children, value, name, selected, options.merge(:level => options[:level] + 1))
      entries
    end
  end
end