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

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.

Solution

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