ruby on rails - Working with instance variables within a model -

i want instantiate "battle" upon creation variables can manipulate without accessing database , first when method calls , calculation has been done, save battle result database. want "player" method return sorted array created in callback, @ moment returns nil

class battle < activerecord::base     after_create       @battlelog = ""       @field = []       @conditions = []       @player = sort_by_initiative(action.character.army.members.map{ |m| [m.unit, m.amount]})               @computer = sort_by_initiative(action.instance.members.map{ |m| [m.unit, m.amount]})     end      # associations     belongs_to :action      def sort_by_initiative(array)         array.sort { |a, b| b.first.initiative <=> a.first.initiative }     end      def player         @player     end 

i think looking attr_accessor :player, (this ruby, see ruby classes more) creates accessible attribute (read , write) on model instance. attr_reader :player give read-only attribute, used if attribute set internal operations. can call this_battle.player on this_battle instance of class battle. remember though these attributes not persist if call other controller actions or render new views unless have way store them permanently.