Question

I am basically looking for a way to implement a polymorphic model Subscription in my app right now

There are entries, users and subscriptions in my app right now. A user can subscribe to an entry. Later on, a user can subscribe to something else. Hence polymorphic.

I have been following the rails cast on polymorphic model. However, I have made some modifications:

  # Param: {"subscribable_type": "entry|something", "subscribable_id": int}
  def create
    @subscribable = find_subscribable(params[:subscription])
    @subscription = @subscribable.subscriptions.build(params[:subscription])
    @subscription.user_id = current_user.id
    if @subscription.save
      redirect_to :back, :notice => "Successfully created subscription."
    else
      redirect_to :back, :notice => "Failed creating subscription."
    end
  end

  def find_subscribable(instance_params)
    class_name = instance_params["subscribable_type"].classify.constantize
    class_name.find(instance_params["subscribable_id"])
  end

and in my models:

class Subscription < ActiveRecord::Base
  attr_accessible :user_id, :subscribable_id, :subscribable_type

  belongs_to :user

  belongs_to :subscribable, :polymorphic => true
end

class Entry < ActiveRecord::Base
  attr_accessible :title, :body, :img, :author_id

  belongs_to :author, :class_name => "User", :foreign_key => "author_id"
  has_many :tidbits
  has_and_belongs_to_many :tags

  has_many :subscriptions, :as => :subscribable
end

class User < ActiveRecord::Base
  # Include default devise modules. Others available are:
  # :token_authenticatable, :encryptable, :confirmable, :lockable, :timeoutable and :omniauthable
  devise :database_authenticatable, :registerable,
         :recoverable, :rememberable, :trackable, :validatable
end

from the console:

1.9.2p290 :037 > Subscription.last
  Subscription Load (0.1ms)  SELECT "subscriptions".* FROM "subscriptions" ORDER BY "subscriptions"."id" DESC LIMIT 1
 => #<Subscription id: 3, user_id: 1, subscribable_id: 3, subscribable_type: "entry", created_at: "2011-12-15 07:17:53", updated_at: "2011-12-15 07:17:53"> 

Somehow, the entry above has no subscriptions:

1.9.2p290 :040 > Entry.find(3).subscriptions
  Entry Load (0.2ms)  SELECT "entries".* FROM "entries" WHERE "entries"."id" = ? LIMIT 1  [["id", 3]]
  Subscription Load (0.2ms)  SELECT "subscriptions".* FROM "subscriptions" WHERE "subscriptions"."subscribable_id" = 3 AND "subscriptions"."subscribable_type" = 'Entry'
 => [] 

What am I doing wrong?

And how should I set up User so that I can access all the user’s entries subscriptions and other forms of subscriptions?

Answer 1

iThe second query is looking for subscribable_type = 'Entry' (upper case), but the output from the first query shows that the persisted data has subscribable_type = 'entry' (lower case).

You need to change whatever us calling the create method such that it passes uppercase Entry.