scope :visible, where(:visible => true)
scope :visible_to, lambda { |u| visible.where("visibility IN ('public', 'identifiable') OR user_id = ?", u) }
scope :public, where(:visibility => ["public", "identifiable"])
+ scope :tagged, lambda { |t| joins(:tags).where(:gpx_file_tags => { :tag => t }) }
validates_presence_of :user_id, :name, :timestamp
validates_presence_of :description, :on => :create