Rails 4 Business Logic, Authorization - Updating Prices based on Authentication

Question

I have a super basic ecommerce app with a User model authenticated with Omniauth, Product model with name and price, and ShoppingCart and ShoppingCartItem models (utilizing the acts_as_shopping_cart gem).

My issue is when I have a user authenticate through an Omniauth provider, I want to provide discounts based on who they authenticate with.

Let's say they sign in with facebook - then I want to provide a 20% discount for them. I'm not sure how to go about this actually - I think I want to write this business logic in my Product and ShoppingCartItem models, setting something like

def self.price 
  if current_user.provider == 'facebook'
    super * 0.8 
  else
    super
end

but I can't access current_user within the models because it is set by the session.

Should I do it in the controller where I have access to current_user? Then I'd have to open the Product and ShoppingCartItem classes within the controllers to override their price methods which all feels wrong and frankly I don't know if it will even work.

Answer 1

I changed my strategy a bit. I decided to create a method to override the total method on my shoppingcart instance. I didn't want to change the prices, I just applied the discount to the total like you would see at the checkout view.

I created an instance method in the model shopping_cart.rb like so:

def discount(user)
  if user && user.provider == 'facebook'
    def total
      super * 0.8
    end
  else
    def total
      super
    end
  end
end

Then I can call this method in the controller and pass in current_user there.

shopping_carts_controller.rb

def show
  @shopping_cart.discount(current_user)
end

And in the view I just have @shopping_cart.total where the total method is overriden based on the user's oauth provider!