Question

I have a 3 simple models:

class User < ActiveRecord::Base
    has_many    :subscriptions
end

class Game < ActiveRecord::Base
    has_many    :subscriptions
end

class Subscription < ActiveRecord::Base
    belongs_to  :user
    belongs_to  :game
end

What I am wondering is, is it possible when I query for Games to include another attribute called ‘is_subbed’ which will contain wether a particular user is subscribed to a game? Something like:

a_user = User.first

games = Game.scoped
games.conditions blah blah blah

and games will include a ‘virtual’ or in memory attribute that will be custom to a_user called is_subed

Answer 1

You can make a class method and an instance method (for a single game) like so:

class Game < ActiveRecord::Base
  def self.subscribed?(user)
    joins(:subscriptions).where(subscriptions: { user_id: user.id}).exists?
  end

  def subscribed?(user)
    subscriptions.where(user_id: user.id).exists?
  end
end

To get this result for each game using the query API, you can do this:

scope :with_subscriptions, lambda do |user|
  joins("LEFT JOIN subscriptions ON subscriptions.game_id = games.id AND subscriptions.user_id = #{user.id}")
  select("games.*, CASE WHEN subscriptions.user_id IS NULL THEN true ELSE false END as is_subscribed")
end

This will give you an is_subscribed parameter on each game object returned.