Ruby-on-rails 处理货币/金钱的最佳方法是什么？

What is the best method of handling currency/money?

提问by Barry Gallagher

I'm working on a very basic shopping cart system.

我正在开发一个非常基本的购物车系统。

I have a table itemsthat has a column priceof type integer.

我有一个表items，其中有一列price类型为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?

对于同时包含欧元和美分的价格，我无法在我的视图中显示价格值。就在 Rails 框架中处理货币而言，我是否遗漏了一些明显的东西？

回答by molf

You'll probably want to use a DECIMALtype in your database. In your migration, do something like this:

您可能希望DECIMAL在数据库中使用类型。在您的迁移中，执行以下操作：

# 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

In Rails, the :decimaltype is returned as BigDecimal, which is great for price calculation.

在 Rails 中，:decimal类型返回为BigDecimal，这对于价格计算非常有用。

If you insist on using integers, you will have to manually convert to and from BigDecimals everywhere, which will probably just become a pain.

如果您坚持使用整数，您将不得不在BigDecimal任何地方手动转换s和从s转换，这可能会变得很痛苦。

As pointed out by mcl, to print the price, use:

正如 mcl 所指出的，要打印价格，请使用：

number_to_currency(price, :unit => "")
#=> 1,234.01

回答by Ken Mayer

Here's a fine, simple approach that leverages composed_of(part of ActiveRecord, using the ValueObject pattern) and the Money gem

这是一个很好的、简单的方法，它利用composed_of（ActiveRecord 的一部分，使用 ValueObject 模式）和 Money gem

You'll need

你需要

• The Money gem(version 4.1.0)
• A model, for example Product
• An integercolumn in your model (and database), for example :price

• 在金钱的宝石（版本4.1.0）
• 一个模型，例如 Product
• 例如integer，模型（和数据库）中的一列:price

Write this in your product.rbfile:

在你的product.rb文件中写下这个：

class Product > ActiveRecord::Base

  composed_of :price,
              :class_name => 'Money',
              :mapping => %w(price cents),
              :converter => Proc.new { |value| Money.new(value) }
  # ...

What you'll get:

你会得到什么：

• 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_sdisplays a decimal formatted number ("1234.00")
• product.price.formatdisplays 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

• 如果没有任何额外的更改，您的所有表单都将显示美元和美分，但内部表示仍然只是美分。表单将接受诸如“$12,034.95”之类的值并为您进行转换。无需向模型或视图中的助手添加额外的处理程序或属性。
• product.price = "$12.00"自动转换为 Money 类
• product.price.to_s显示十进制格式的数字（“1234.00”）
• product.price.format显示正确格式的货币字符串
• 如果您需要发送美分（到需要便士的支付网关）， product.price.cents.to_s
• 免费货币兑换

回答by alex.zherdev

Common practice for handling currency is to use decimal type. Here is a simple example from "Agile Web Development with Rails"

处理货币的常见做法是使用十进制类型。这是“使用 Rails 进行敏捷 Web 开发”中的一个简单示例

add_column :products, :price, :decimal, :precision => 8, :scale => 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

这将允许您处理从 -999,999.99 到 999,999.99 的价格
您可能还希望在您的项目中包含一个验证，例如

def validate 
  errors.add(:price, "should be at least 0.01") if price.nil? || price < 0.01 
end 

to sanity-check your values.

理智检查你的价值观。

回答by The Whiz of Oz

If you are using Postgres (and since we're in 2017 now) you might want to give their :moneycolumn type a try.

如果您正在使用 Postgres（并且因为我们现在是 2017 年），您可能想:money尝试一下他们的列类型。

add_column :products, :price, :money, default: 0

回答by Troggy

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

使用money-rails gem。它可以很好地处理您模型中的货币和货币，并且还有一堆帮助程序来格式化您的价格。

回答by Thomas Klemm

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.

使用虚拟属性（链接到修订（付费）Railscast），您可以将 price_in_cents 存储在整数列中，并在您的产品模型中添加虚拟属性 price_in_dollars 作为 getter 和 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.

来源：RailsCasts #016：虚拟属性：虚拟属性是添加不直接映射到数据库的表单字段的一种干净方式。在这里，我将展示如何处理验证、关联等。

回答by Zlatko Alomerovic

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.

对于一些有抱负的 RoR 开发的初级/初学者来说，只是一点点更新和所有答案的凝聚力，他们肯定会来这里做一些解释。

Working with money

用钱工作

Use :decimalto store money in the DB, as @molf suggested (and what my company uses as a golden standard when working with money).

使用:decimal存储钱DB，作为@molf建议（什么我公司使用的金标准与金钱工作时）。

# 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:

几点：

• :decimalis going to be used as BigDecimalwhich solves a lot of issues.

• precisionand scaleshould be adjusted, depending on what you are representing

  • If you work with receiving and sending payments, precision: 8and scale: 2gives you 999,999.99as 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.

• :decimal将用于BigDecimal解决很多问题。

• precision并且scale应该根据您所代表的内容进行调整

  • 如果您处理接收和发送付款，precision: 8并将scale: 2您999,999.99作为最高金额，则在 90% 的情况下都可以。

  • 如果您需要表示财产或稀有汽车的价值，则应使用更高的precision.

  • 如果您使用坐标（经度和纬度），您肯定需要更高的scale.

How to generate a migration

如何生成迁移

To generate the migration with the above content, run in terminal:

要使用上述内容生成迁移，请在终端中运行：

bin/rails g migration AddPriceToItems price:decimal{8-2}

or

或者

bin/rails g migration AddPriceToItems 'price:decimal{5,2}'

as explained in this blogpost.

如本博文中所述。

Currency formatting

货币格式

KISSthe extra libraries goodbye and use built-in helpers. Use number_to_currencyas @molf and @facundofarias suggested.

KISS额外库再见，使用内置的助手。使用number_to_currency@molf 和@facundofarias 建议。

To play with number_to_currencyhelper in Rails console, send a call to the ActiveSupport's NumberHelperclass in order to access the helper.

要number_to_currency在 Rails 控制台中使用helper，请向ActiveSupport'sNumberHelper类发送调用以访问 helper。

For example:

例如：

ActiveSupport::NumberHelper.number_to_currency(2_500_000.61, unit: '', precision: 2, separator: ',', delimiter: '', format: "%n%u")

gives the following output

给出以下输出

2500000,61

Check the other optionsof number_to_currencyhelper.

检查其他options的number_to_currency帮手。

Where to put it

把它放在哪里

You can put it in an application helper and use it inside views for any amount.

您可以将它放在应用程序助手中，并在视图中以任意数量使用它。

module ApplicationHelper    
  def format_currency(amount)
    number_to_currency(amount, unit: '', precision: 2, separator: ',', delimiter: '', format: "%n%u")
  end
end

Or you can put it in the Itemmodel as an instance method, and call it where you need to format the price (in views or helpers).

或者你可以把它Item作为一个实例方法放在模型中，并在你需要格式化价格的地方调用它（在视图或助手中）。

class Item < ActiveRecord::Base
  def format_price
    number_to_currency(price, unit: '', precision: 2, separator: ',', delimiter: '', format: "%n%u")
  end
end

And, an example how I use the number_to_currencyinside a contrroler (notice the negative_formatoption, used to represent refunds)

并且，我如何使用number_to_currency控制器内部的示例（请注意该negative_format选项，用于表示退款）

def refund_information
  amount_formatted = 
    ActionController::Base.helpers.number_to_currency(@refund.amount, negative_format: '(%u%n)')
  {
    # ...
    amount_formatted: amount_formatted,
    # ...
  }
end

回答by jethroo

If someone is using Sequel the migration would look something like:

如果有人使用 Sequel，迁移将类似于：

add_column :products, :price, "decimal(8,2)"

somehow Sequel ignores :precision and :scale

不知何故 Sequel 忽略了 :precision 和 :scale

(Sequel Version: sequel (3.39.0, 3.38.0))

（续集版本：续集（3.39.0、3.38.0））

回答by Brent Royal-Gordon

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:

我的底层 API 都使用美分来表示金钱，我不想改变这一点。我也没有用大量的钱工作。所以我只是把它放在一个辅助方法中：

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.

这会将整数转换为至少包含三位数字的字符串（如有必要，添加前导零），然后在最后两位数字之前插入一个小数点，从不使用Float. 从那里您可以添加适合您的用例的任何货币符号。

It's definitelyquick and dirty, but sometimes that's just fine!

它绝对又快又脏，但有时这很好！

回答by facundofarias

I am using it on this way:

我正在以这种方式使用它：

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.

当然，货币符号、精度、格式等取决于每种货币。