Question

I’m a fairly new Rails developer, and I have an existing application that I’m trying to add a new model to (Ability) that has an association to an existing model (Champion). I have it setup to what makes sense to me logically the way I understand the “has_one” and “belongs_to” mechanics, but I’m only getting the same one record back for each has_one relationship in each Champion.

Here’s the setup:

The existing model is called Champion, and I’m creating a new Ability model that is part of the Champion model. I want to organize the Champion model so that it has 5 abilities named “q”, “w”, “e”, “r”, and “passive”. Each ability will only ever belong to one champion.

Here’s my migration that adds a new Ability object with a champion_id for the belongs_to association:

class CreateAbilities < ActiveRecord::Migration
  def change
    create_table :abilities do |t|
      t.integer :champion_id
      t.timestamps
    end
  end
end

Here is the migration that adds the ability references to the Champion model:

class AddAbilitiesToChampions < ActiveRecord::Migration
  def change
    add_column :champions, :q, :integer
    add_column :champions, :w, :integer
    add_column :champions, :e, :integer
    add_column :champions, :r, :integer
    add_column :champions, :passive, :integer
  end
end

Ability.rb model:

class Ability < ActiveRecord::Base
  attr_accessible :ability_description,
                  :cost,
                  :effect,
                  :cooldown,
                  :range,
                  :name,
                  :icon,
                  :champion_id

  belongs_to :champion
end

Champion.rb model:

class Champion < ActiveRecord::Base
  attr_accessible :champion_id,
                  :q,
                  :w,
                  :e,
                  :r,
                  :passive

  has_one :q, :class_name => "Ability"
  has_one :w, :class_name => "Ability"
  has_one :e, :class_name => "Ability"
  has_one :r, :class_name => "Ability"
  has_one :passive, :class_name => "Ability"
end

Now that this point I have a model that seems to be creating the relationships correctly, however when I view the output on the server its performing the same select statement for every ability association, and selecting the same record each time.

Started GET "/champions.json" for 127.0.0.1 at 2013-01-08 15:13:30 -0700
Processing by ChampionsController#index as JSON
  Champion Load (0.5ms)  SELECT "champions".* FROM "champions" 
  Item Load (0.4ms)  SELECT "items".* FROM "items" 
  Spell Load (0.3ms)  SELECT "spells".* FROM "spells" 
  Mastery Load (0.3ms)  SELECT "masteries".* FROM "masteries" 
  CACHE (0.0ms)  SELECT "champions".* FROM "champions" 
  Ability Load (0.6ms)  SELECT "abilities".* FROM "abilities" WHERE "abilities"."champion_id" = 1 LIMIT 1
  CACHE (0.0ms)  SELECT "abilities".* FROM "abilities" WHERE "abilities"."champion_id" = 1 LIMIT 1
  CACHE (0.0ms)  SELECT "abilities".* FROM "abilities" WHERE "abilities"."champion_id" = 1 LIMIT 1
  CACHE (0.0ms)  SELECT "abilities".* FROM "abilities" WHERE "abilities"."champion_id" = 1 LIMIT 1
  CACHE (0.0ms)  SELECT "abilities".* FROM "abilities" WHERE "abilities"."champion_id" = 1 LIMIT 1
  Ability Load (0.2ms)  SELECT "abilities".* FROM "abilities" WHERE "abilities"."champion_id" = 2 LIMIT 1
  CACHE (0.0ms)  SELECT "abilities".* FROM "abilities" WHERE "abilities"."champion_id" = 2 LIMIT 1
  CACHE (0.0ms)  SELECT "abilities".* FROM "abilities" WHERE "abilities"."champion_id" = 2 LIMIT 1
  CACHE (0.0ms)  SELECT "abilities".* FROM "abilities" WHERE "abilities"."champion_id" = 2 LIMIT 1
  CACHE (0.0ms)  SELECT "abilities".* FROM "abilities" WHERE "abilities"."champion_id" = 2 LIMIT 1
Completed 200 OK in 111ms (Views: 47.4ms | ActiveRecord: 12.8ms)

How do I modify my setup so the select statement chooses the correct ability for each of these attributes? I’ve tried the inverting the relationship without much success. Any help is appreciated!

EDIT: Here’s the code in my champions_controller.rb which serves the JSON for the model:

class ChampionsController < ApplicationController
  before_filter :find_champions

  def find_champions
    @champions = Champion.all
  end

  def index
    respond_to do |format|
      format.json { render :json => { "champions" => @champions }}
    end
  end
end

Answer 1

Give this a go in the Champion model. With belongs_to the foreign_key will be on the model you define the relationship in, has_one will look in the model you associate with.

belongs_to :q, :class_name => "Ability", :foreign_key => "q" 
belongs_to :w, :class_name => "Ability", :foreign_key => "w"
belongs_to :e, :class_name => "Ability", :foreign_key => "e" 
belongs_to :r, :class_name => "Ability", :foreign_key => "r" 

More info.