What is the best method of handling currency money

Question

I m working on a very basic shopping cart system    I have a table items that has a column price of type integer    I m having trouble displaying the price value in my views for prices that include both Euros and cents  Am I missing something obvious as far as handling currency in the Rails framework is concerned

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You can pass some options to number to currency  a standard Rails 4 view helper    number to currency 12 0   precision   gt  2      gt    12 00    As posted by Dylan Markow

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My underlying APIs were all using cents to represent money  and I didn t want to change that  Nor was I working with large amounts of money  So I just put this in a helper method   sprintf   03d   amount  insert -3         That converts the integer to a string with at least three digits  adding leading zeroes if necessary   then inserts a decimal point before the last two digits  never using a Float  From there you can add whatever currency symbols are appropriate for your use case   It s definitely quick and dirty  but sometimes that s just fine

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Here s a fine  simple approach that leverages composed of  part of ActiveRecord  using the ValueObject pattern  and the Money gem   You ll need   The Money gem  version 4 1 0   A model  for example Product An integer column in your model  and database   for example  price   Write this in your product rb file   class Product  gt  ActiveRecord  Base    composed of  price                 class name   gt   Money                  mapping   gt   w price cents                  converter   gt  Proc new    value  Money new value              What you ll get    Without any extra changes  all of your forms will show dollars and cents  but the internal representation is still just cents  The forms will accept values like   12 034 95  and convert it for you  There s no need to add extra handlers or attributes to your model  or helpers in your view  product price     12 00  automatically converts to the Money class product price to s displays a decimal formatted number   1234 00   product price format displays a properly formatted string for the currency If you need to send cents  to a payment gateway that wants pennies   product price cents to s Currency conversion for free

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If you are using Postgres  and since we re in 2017 now  you might want to give their  money column type a try   add column  products   price   money  default  0

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Using Virtual Attributes  Link to revised paid  Railscast  you can store your price in cents in an integer column and add a virtual attribute price in dollars in your product model as a getter and setter     Add a price in cents integer column   rails g migration add price in cents to products price in cents integer    Use virtual attributes in your Product model   app models product rb  def price in dollars   price in cents to d 100 if price in cents end  def price in dollars  dollars    self price in cents   dollars to d 100 if dollars present  end   Source  RailsCasts  016  Virtual Attributes  Virtual attributes are a clean way to add form fields that do not map directly to the database  Here I show how to handle validations  associations  and more

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Simple code for Ruby  amp  Rails   lt    number to currency 1234567890 50    gt   OUT PUT   gt   1 234 567 890 50

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If someone is using Sequel the migration would look something like    add column  products   price   decimal 8 2     somehow Sequel ignores  precision and  scale   Sequel Version  sequel  3 39 0  3 38 0

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Use money-rails gem  It nicely handles money and currencies in your model and also has a bunch of helpers to format your prices

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You ll probably want to use a DECIMAL type in your database  In your migration  do something like this     precision is the total number of digits   scale is the number of digits to the right of the decimal point add column  items   price   decimal   precision   gt  8   scale   gt  2   In Rails  the  decimal type is returned as BigDecimal  which is great for price calculation   If you insist on using integers  you will have to manually convert to and from BigDecimals everywhere  which will probably just become a pain   As pointed out by mcl  to print the price  use   number to currency price   unit   gt            gt     1 234 01

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Definitely integers   And even though BigDecimal technically exists 1 5 will still give you a pure Float in Ruby

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Just a little update and a cohesion of all the answers for some aspiring juniors beginners in RoR development that will surely come here for some explanations  Working with money Use  decimal to store money in the DB  as  molf suggested  and what my company uses as a golden standard when working with money     precision is the total number of digits   scale is the number of digits to the right of the decimal point add column  items   price   decimal  precision  8  scale  2  Few points    decimal is going to be used as BigDecimal which solves a lot of issues   precision and scale should be adjusted  depending on what you are representing  If you work with receiving and sending payments  precision  8 and scale  2 gives you 999 999 99 as the highest amount  which is fine in 90  of cases   If you need to represent the value of a property or a rare car  you should use a higher precision   If you work with coordinates  longitude and latitude   you will surely need a higher scale      How to generate a migration To generate the migration with the above content  run in terminal  bin rails g migration AddPriceToItems price decimal 8-2   or bin rails g migration AddPriceToItems  price decimal 5 2    as explained in this blog post  Currency formatting KISS the extra libraries goodbye and use built-in helpers  Use number to currency as  molf and  facundofarias suggested  To play with number to currency helper in Rails console  send a call to the ActiveSupport s NumberHelper class in order to access the helper  For example  ActiveSupport  NumberHelper number to currency 2 500 000 61  unit         precision  2  separator       delimiter      format   quot  n u quot    gives the following output 2500000 61     Check the other options of number to currency helper  Where to put it You can put it in an application helper and use it inside views for any amount  module ApplicationHelper       def format currency amount      number to currency amount  unit         precision  2  separator       delimiter      format   quot  n u quot     end end  Or you can put it in the Item model as an instance method  and call it where you need to format the price  in views or helpers   class Item  lt  ActiveRecord  Base   def format price     number to currency price  unit         precision  2  separator       delimiter      format   quot  n u quot     end end  And  an example how I use the number to currency inside a contrroler   notice the negative format option  used to represent refunds  def refund information   amount formatted        ActionController  Base helpers number to currency  refund amount  negative format     u n                      amount formatted  amount formatted                end

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Common practice for handling currency is to use decimal type  Here is a simple example from  Agile Web Development with Rails   add column  products   price   decimal   precision   gt  8   scale   gt  2    This will allow you to handle prices from -999 999 99 to 999 999 99 You may also want to include a validation in your items like   def validate    errors add  price   should be at least 0 01   if price nil     price  lt  0 01  end    to sanity-check your values

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I am using it on this way   number to currency amount  unit         precision  2  format    u  n     Of course that the currency symbol  precision  format and so on depends on each currency

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