I18n date/number parsing/localization

I18nAlchemy aims to handle date, time and number parsing, based on current I18n locale format. The main idea is to have ORMs, such as ActiveRecord for now, to automatically accept dates/numbers given in the current locale format, and return these values localized as well.

Almost all projects I've been working so far required some sort of input using dates and numbers, and it has always been a pain due to lack of this support in ActiveRecord itself. As I do most of my projects using different date/number formats than the English defaults (I live in Brazil), we've been adopting different ways to handle that in each application.

I've already used the delocalize gem in some of these projects, and validates_timeliness parser in others, and both work pretty well actually. But I think it might work a bit different than delocalize, and mainly, I wanted to learn more about I18n and ActiveRecord internals.

I18nAlchemy is pretty straigthforward to use, you just need to include it in your ActiveRecord model. Lets say we are working with a Product model:

class Product < ActiveRecord::Base
  include I18n::Alchemy
end

By mixing the module into your model, you get the localized method:

@product   = Product.first
@localized = @product.localized

Here are some examples on how to use it with numeric values:

@localized.price = "1.99"

@product.price   # => 1.99
@localized.price # => "1.99"

I18n.with_locale :pt do
  @localized.price = "1,88"

  @product.price   # => 1.88
  @localized.price # => "1,88"
end

Please notice that the localized proxy also formats your numeric values based on the current precision in your I18n locale file:

@product.price = 1.3
@localized.price # => "1.30", considering a precision of 2

And with thousand separators as well:

@product.price = 1840.32
@localized.price # => "1,840.32", considering separator = "," and delimiter = "."

Some examples with date / time objects:

@localized.released_at = "12/31/2011"

@product.released_at   # => Date.new(2011, 12, 31)
@localized.released_at # => "12/31/2011"

I18n.with_locale :pt do
  @localized.released_at = "31/12/2011"

  @product.released_at   # => Date.new(2011, 12, 31)
  @localized.released_at # => "31/12/2011"
end

The localized method quacks like ActiveRecord: you can give a hash of attributes and extra options if you want, and it will delegate everything to the object, parsing the attributes before:

# This will parse the attributes in the given hash.
I18n.with_locale :pt do
  @localized = @product.localized(:price => "1,88")

  @product.price   # => 1.88
  @localized.price # => "1,88"
end

Given a product model with a total method, that is a simple calculation of quantity * price, you can tell I18n::Alchemy to localize that method for you together with the attributes:

class Product < ActiveRecord::Base
  include I18n::Alchemy
  localize :total, :using => :number

  def total
    quantity * price
  end
end

@product          = Product.first
@product.price    = 1.99
@product.quantity = 10

@product.total   # => 19.90
@localized.total # => "19,90"

If the method has a writer method, in this case total=, that'd get a parsed version for input values as well.

With localize is possible to localize objects that aren't inheriting from ActiveRecord::Base, as long that your class have both reader and writer methods available:

class Product
  include I18n::Alchemy
  localize :released_at, :using => :date

  attr_accessor :released_at
end

If you want to customize the way an attribute is parsed/localized, you can create a custom parser that looks like this:

module MyCustomDateParser
  include I18n::Alchemy::DateParser
  extend self

  def localize(value)
    I18n.localize value, :format => :custom
  end

  protected

  def i18n_format
    I18n.t(:custom, :scope => [:date, :formats])
  end
end

And then just configure the attribute you want to use with this new parser:

class Product < ActiveRecord::Base
  include I18n::Alchemy
  localize :released_month, :using => MyCustomDateParser
end

By doing this, I18n::Alchemy will be set up to use your custom parser for that particular attribute, which in this case will make use of the :custom date format in your i18n locale.

If you are using localize, you can mix the custom parsers with your existing configuration:

class Product < ActiveRecord::Base
  include I18n::Alchemy
  localize :total, :using => MyCustomNumberParser
end

Right now the lib uses the same configuration for numeric, date and time values from Rails:

en:

  date:
    formats:
      default: "%m/%d/%Y"

  time:
    formats:
      default: "%m/%d/%Y %H:%M:%S"

  number:
    format:
      separator: '.'
      delimiter: ','
      precision: 2

Please notice the default date and time format is considered for input values for now, and it will only accept valid values matching these formats. We plan to add specific formats and to parse a list of possible input formats for I18nAlchemy, to make it more flexible, please refer to TODO file for more info.

Carlos Antonio da Silva (http://github.com/carlosantoniodasilva)

MIT License.