Question

I can’t get my subscription to update with my product and also duplicate the attributes of the product to the same fields as my subscription table.

My associations are, subscriptions and products belong to a User but a Product has many subscriptions.

Subscription.rb

class Subscription
  belongs_to :subscriber, :class_name => "User"
  belongs_to :subscribable, :polymorphic => true
end

Product.rb

class Product
  belongs_to :user
  has_many :subscriptions, :as => :subscribable, :dependent => :destroy
end

User.rb

class User
  has_many :products, :dependent => :destroy
  has_many :subscriptions, :foreign_key => :subscriber_id, :dependent => :destroy
end

Then the Product and Subscription table with the same columns that I’m trying to duplicate:

create_table :products do |t|
   t.string  :name
   t.decimal :price
   t.integer :user_id
end

create_table :subscriptions do |t|
   t.string  :name
   t.decimal :price
   t.integer :subscriber_id # same as user_id
   t.integer :subscribable_id
   t.string  :subscribable_type
end

ProductsController

def edit
   @product = Product.find(params[:id])
end

def update
   @product = Product.find(params[:id])
   if @product.update_attributes(params[:product])
      redirect_to(@product, :notice => 'Successfully Updated.')   
   else 
      render :back
   end
end

ProductObserver

class ProductObserver < ActiveRecord::Observer
  def after_update(product)
    if self.subscriptions.find_by_subscribable_id_and_subscribable_type(subscribable_id, subscribable_type)
        subscription = Subscription.find_by_subscribable_id_and_subscribable_type(subscribable_id, subscribable_type)
        self.subscription.update_attributes(params[:subscription]).select{ |key, _| Subscription.attribute_names.include? key })
    end
  end
end

What the after_update is suppose to do is:

1. Check if a subscription for the particular product exist and if it does….
2. Update the current users subscription with the products new edited attributes.

Right now, the Subscription doesn’t update when the Product does. What do I need to fix about this code to get it to do this? What about when duplicating the product fields to its subscription?

Answer 1

Not sure if that was just a typo, but your observer is wrong. self is not your product in an observer. Instead you should use product (the given parameter) instead.

Secondly your lookup of the subscriptions seems wrong too. You are using subscribable_id and subscribable_type which are not defined and thus just nil. I think you want to use product.id and 'Product', but then you could just iterate over all subscriptions of the product. product.subscriptions returns all subscriptions linked to that product.

Lastly, if you are going to keep price and name of a subscription always in sync with the linked product, why do not something like this instead:

 create_table :products do |t|
   t.string  :name
   t.decimal :price
   t.integer :user_id
end

create_table :subscriptions do |t|
   t.integer :subscriber_id # same as user_id
   t.integer :subscribable_id
   t.string  :subscribable_type
end

and inside your subscription model do

class Subscription
  belongs_to :subscriber, :class_name => "User"
  belongs_to :subscribable, :polymorphic => true

  delegate :name, :price, :to => :subscribable, :allow_nil => true
end

Hope this helps.