ruby - Rails NoMethodError when calling method on parent -

playing around single table inheritance , hstore in rails 4 getting error when trying call method in parent:

# models/item.rb class item < activerecord::base   def getter_setter_for(key)     define_method(key)       properties && properties[key]     end      define_method("#{key}=") |value|       self.properties = (properties || {}).merge(key => value)     end   end end  # models/disk_item.rb class diskitem < item   %w[filename path].each |key|     getter_setter_for(key)               ##  <== error calling method   end end 

error:

exception encountered: #<nomethoderror: undefined method `getter_setter_for' #<class:0x007f8c739a5ae0>> 

what obvious thing have overlooked?

getter_setter_for(key) instance method. getting called @ class level. called during diskitem class load on class scope.