How to configure money-rails gem to work with higher precision than 4 digits

Question

We are using money-rails gem in our application. Until now, we were OK with 4 decimal digits precision, but we need to switch to 6. Unfortunately I'm unable to store higher precision numbers into Postgres - number is rounded before saving.

class MyModel < ApplicationRecord
  monetize :price_cents # :price_cents, :decimal, default: 0, precision: 30, scale: 10
end

Money itself seems to work fine with higher precision

pry(main)> Money.new(181.123456789).to_f
=> 1.81123456789

Testing model in console. All works fine before save.

my_model = MyModel.find(1)
my_model.price = Money.new(181.123456789)
my_model.price.to_f # => 1.81123456789
my_model.save
my_model.price.to_f # => 1.8112

And the ActiveRecord output says the trimmed number is actually being send to database. (notice the 181.12).

UPDATE "my_models" SET "price_cents" = $1 ... [["price_cents", "181.12"] ...]

Is there any way to allow money-rails gem to work with more precision? It seems like Money gem has no problem with higher precision on its own.

Answer 1

That behavior comes from money rounding, to turn it off, use:

Money.infinite_precision = true

here's test:

require "bundler/inline"

gemfile(ENV['INSTALL']=='1') do
  source "https://rubygems.org"
  gem "rails", '~>6.0'
  gem "sqlite3"
  gem 'money-rails'
end

require "minitest/autorun"
require "logger"
require "active_record"
require 'money-rails'

ActiveRecord::Base.establish_connection(adapter: "sqlite3", database: ":memory:")
ActiveRecord::Base.logger = Logger.new(STDOUT)
ActiveRecord::Schema.define do
  create_table(:models, force: true){|t| t.decimal :price_cents, default: 0, precision: 30, scale: 10 }
end

# to remove config warnings:
Money.locale_backend = :currency
Money.default_currency= :usd

# actual fix:
Money.infinite_precision = true

MoneyRails::Hooks.init # in a normal app is called automatically


class Model < ActiveRecord::Base
  monetize :price_cents 
end

class BugTest < Minitest::Test
  def test_association_stuff
    m = Model.create!(price_cents: 181.123456789).reload
    assert_equal 181.123456789, m.price_cents
    assert_equal 1.81123456789, m.price.to_f

    m2 = Model.create(price: Money.new(182.123456789)).reload
    assert_equal 1.82123456789, m2.price.to_f
  end
end