money-rails gem column naming conventions

Question

I have an Order model with unit_price, discount_price, final_price etc.. All are integer fields in postgres db. Currently its rounding amount to the next integer and saves that. But now I found that this is not a good approach as it might cause some errors/issues in future. So I planned to save money values in penny by doing(USD*100) but when displaying shows it in GBP by writing some helpers.

But I found this gem now money-rails which could do what I want. I am trying to wrap my head around this gem,but I cant really figure out some conventions used here also not sure its suitable for my purpose

My default currency is GBP.

I can see that this gem uses the convention _cents by default

monetize :price_cents #from docs

Above assume a db column price_cents. Here why we should use cents as a static column? Whats the purpose of that? Other than being explicit any other uses here?

If its for a purpose like for cents it automatically look for USD, if penny looks for GBP & soforth... then for each currency our app supports we will endup creating new db columns like price_penny, price_cent etc.. which is not that great if there are lot of currencies. Or can I use a generic name here like price_smallest and use this regardless of currecy type? Also

I cant figure out the exact usecase here properly. Could someone shed some light into this topic?

Note: My app doesn't have plans for supporting other currencies now. But could be added in future. So good to consider that now I think..

Answer 1

So you need to remove the columns unit_price, discount_price, final_price from the table orders. And add them back correctly with add_monetize.

create a new migration file that looks like this:

class FixPricesInOrders < ActiveRecord::Migration[5.0]
  def change
    # Remove Columns
    remove_column :orders, :unit_price
    remove_column :orders, :discount_price
    remove_column :orders, :final_price
    # Add money
    add_monetize :orders, :unit_price
    add_monetize :orders, :discount_price
    add_monetize :orders, :final_price
  end
end

From https://github.com/RubyMoney/money-rails

"Due to the addition of the money column type for PostgreSQL in Rails 4.2, you will need to use add_monetize instead of add_money column."

Then make sure you add the following to app/models/order.rb

monetize :unit_price
monetize :discount_price
monetize :final_price