armor_item.rb

class ArmorItem < ActiveRecord::Base
  attr_accessible :armor_tier_id, :bonus_id, :enchant_id, :name, :stat_set_id
  
  belongs_to :armor_tier
  belongs_to :enchant
  belongs_to :bonus
  belongs_to :stat_set
  
  attr_reader :stat, :agility
  
  def stat
    StatSet.find(stat_set_id)
  end
  
  def agility
    ArmorTier.find(armor_tier_id).agility + StatSet.find(stat_set_id).agility
  end
  
  # NoMethodError: undefined method `agility' for #<ArmorTier:0x007fdf7ac7e410>
  
end

gistfile1.txt

1.9.3p194 :004 > character.armor.hands
  ArmorItem Load (0.1ms)  SELECT "armor_items".* FROM "armor_items" WHERE "armor_items"."id" = ? LIMIT 1  [["id", 1]]
 => #<ArmorItem id: 1, armor_tier_id: "2", enchant_id: "", bonus_id: "", created_at: "2012-08-29 01:23:00", updated_at: "2012-08-29 01:44:51", name: "Gloves", stat_set_id: 1> 

1.9.3p194 :003 > character.armor.hands.agility
  ArmorItem Load (0.2ms)  SELECT "armor_items".* FROM "armor_items" WHERE "armor_items"."id" = ? LIMIT 1  [["id", 1]]
  ArmorTier Load (0.2ms)  SELECT "armor_tiers".* FROM "armor_tiers" WHERE "armor_tiers"."id" = ? LIMIT 1  [["id", "2"]]
NoMethodError: undefined method `agility' for #<ArmorTier:0x007fdf7ac7e410>