My first shot at keeping reference associations up to date

mongoid_model_update_attr.rb

class Layer
...blah....
# having to ovewrite update_attributes to make sure the associations get set
  def update_attributes(attr)
    update_map_config_ids(attr[:map_config_ids]) unless attr[:map_config_ids].nil?
    update_layer_type_id(attr[:layer_type_id]) unless attr[:layer_type_id].nil?
    super
  end
  
  private
    def update_map_config_ids(map_config_ids)
      map_config_ids.delete("")
      self.map_config_ids = map_config_ids.uniq
      self.map_config_ids.each do |mc_id|
        mc = project.map_configs.find(mc_id)
        mc.layer_ids<<self.id unless mc.layer_ids.include?(self.id)
        mc.save
      end
    end
    def update_layer_type_id(layer_type_id)
      self.layer_type_id=layer_type_id
      lt = LayerType.find(layer_type_id)
      lt.layer_ids ||= []
      lt.layer_ids<<self.id unless lt.layer_ids.include?(self.id)
      lt.save
    end
end