Mo Money Mo Problems (with ruby)

Are you thinking or starting to build an app that deals with money? Come to this talk to learn the best practices of handling money transactions. In my 2+ years working in a startup based on payments, I have been able to compile do's and don'ts of handling money.

Transcript

1. Mo Money Mo Problems with Ruby
2. Federico @fedesoria
4. Pay By Group CTO
6. Mo Money Mo Problems with Ruby
8. DO's and DONT'S with !
9. ! + database
10. > 1.03 - 0.42 # => 0.61
11. > 1.03 - 0.42 # => 0.61 => 0.6100000000000001
12. Float The formulaic representation which approximates a real number so as to support a trade-off between range and precision 1. 1 https://en.wikipedia.org/wiki/IEEEfloatingpoint
13. 1/3
14. DON'T ! FLOAT
15. DO ! Integer
16. Save everything in cents 1000 => $10
17. BigDecimal ❗ There are some performance issues.
18. ! Rounding
19. $20.005
20. Round down (floor) Round up (ceiling)
21. Round down (floor) Round up (ceiling) Round towards zero (truncate) Round away from zero Round to nearest Round half up Round half down Round half towards zero Round half away from zero Round half to even Round half to odd Stochastic rounding Round half alternatingly Rounding to a logarithmic scale ...
22. Round down (floor) Round up (ceiling) Round towards zero (truncate) Round away from zero Round to nearest Round half up Round half down Round half towards zero Round half away from zero Round half to even Round half to odd Stochastic rounding Round half alternatingly Rounding to a logarithmic scale ...
23. Round half to even Banker's rounding IEEE 754 1 1 https://en.wikipedia.org/wiki/IEEEfloatingpoint
24. > $20.005 => $20.00
25. > $20.015 => $20.02
26. DO ! ROUND_HALF_EVEN
27. BigDecimal.mode(BigDecimal::ROUND_MODE, ROUND_HALF_EVEN)
28. BigDecimal.mode(BigDecimal::ROUND_MODE, :banker)
29. Integer != Float
30. # integer / integer 9 / 5 #=> 1 # float / integer 9.0 / 5 #=> 1.8 # integer / float 9 / 5.0 #=> 1.8
31. ! " #
32. ! " #
33. ! Save the current exchange rate
35. !
36. class Money # Make it rain end
37. gem install money
38. require 'money' require 'money/bank/google_currency' # 10.00 USD money = Money.new(1000, "USD") money.cents #=> 1000 money.currency #=> Currency.new("USD") money.format #=> "$10.00"
39. money = Money.new(1000, "USD") Money.default_bank = Money::Bank::GoogleCurrency.new money.exchange_to("MXN") #=> Money.new(17000, "MXN")
40. # Monkey patch class Money def *(value) if value.is_a? Float raise ArgumentError, "Don't mix Float with money" else super end end end
41. ! Background job is your friend
42. # Example using ActiveJob class PaymentJob < ActiveJob::Base queue_as :default def perform(*payment) # Code to run the payment end end PaymentJob.perform_later @payment
43. DON'T ! 5.times.map do |i| Thread.new do tom.capture(100) sam.payout(100) end end
44. ! Atomic Operations
45. ActiveRecord::Transaction Mutex
46. # Using Rails Account.transaction do tom.capture(100) sam.payout(100) end
47. @lock = Mutex.new @total_captured = 0 @lock.synchronize do @total_captured += tom.capture(100) # => 100 @total_captured += mary.capture(200) # => 200 puts @total_captured # => 300 sam.payout(@total_captured) end
48. ! Be mindful of timestamps
49. ! Keep a ledger
50. class TransactionCopy def readonly? true end end
51. Delete cards?
52. Delete gateways?
53. PaymentTransaction.transaction do Stripe.capture 1000, @credit_card end
54. Stripe Authorize.net PayPal Braintree ...
55. Credit Cards Debit Cards Bitcoin PayPal Doge ACH ...
56. ! Decouple
57. PaymentTransaction.transaction do @gateway.capture 1000, @payment_source end
58. ! " Fraud Detection
59. Use social media Check for IP address vs origin of country of card You can tell from where the card is from using the first 6 digits http://www.binlist.net/
60. Thank you! @fedesoria
61. We are hiring! Pay By Group