Customise database entries for every user - ruby-on-rails

Question

I have an e-commerce site where pricing for the prices are referenced in the prices table under the pricing model.
However, how can i be able to customise prices for individual clients for the same goods. How can i do that using the Price model.
I have tried adding user_id to the table but it seems have to price the same good for every individual client. How can i go about that?
The current table looks like this;
create_table "prices", :force => true do |t|
t.string "country"
t.string "network"
t.decimal "price_euros", :precision => 10, :scale => 3
t.datetime "created_at", :null => false
t.datetime "updated_at", :null => false
t.decimal "price_ugx", :precision => 10, :scale => 3
t.decimal "price_kes", :precision => 10, :scale => 3
t.decimal "price_tzs", :precision => 10, :scale => 3
t.decimal "price_usd", :precision => 10, :scale => 3
end

Answer 1

There are various ways of achieving this. If each customer had the same discount across all goods, then you could add a discount attribute to the User model and apply this to the displayed prices.
If you want unique prices across the products which are unique for each user, then I would create a new model called UserPrice and have 3 attributes: user_id, product_id, price.
I would then have a method in my Product model called price_for_user along the following lines:
def price_for_user(user)
UserPrice.find_by_user_id_and_product_id(user.id,self.id).price
end
When iterating over your products in the view, you could write:
<%= #product.price_for_user(current_user) %>
Obviously, you'll need to adjust variables as required for your situation. I would also index the user_id and product_id columns in the UserPrice table for speed.
NB: If it was me, in my controller, I would also consider looking up all UserPrices by user and creating a hash and then in the view displaying the price by doing a lookup in the hash. This might be quicker.
def index
#products = Product.all
#user_prices = UserPrice.where(user_id: current_user.id).index_by(&:product_id)
end
In your view:
<%= #user_prices[product.id].price %>