Model Translation Layer

model_translator_idea.rb

require 'ostruct'

class String
  def underscore
    self.gsub(/::/, '/').
    gsub(/([A-Z]+)([A-Z][a-z])/,'\1_\2').
    gsub(/([a-z\d])([A-Z])/,'\1_\2').
    tr("-", "_").
    downcase
  end
end

class ApiService
  def self.call
    {
      "Id"               => 1234,
      "ServiceName"      => "foo-bar",
      "Description"      => "foo bar baz",
      "IgnoredAttribute" => 5678
    }
  end
end

# ModelTranslator has two jobs:
#
# 1. Translate CamelCase string keys to underscore symbols.
# 2. Set up hooks for model translators to have more control over
#    their underlying data structure.
#
module ModelTranslator
  def self.included(base)
    base.class_eval do
      extend ClassMethods

      attr_accessor :attributes
    end
  end

  module ClassMethods
    def rename(attr, options={})
      renamed_attributes[attr] = options[:to]
    end

    def ignore(*attr)
      ignored_attributes.concat(attr)
    end

    def call(raw_data)
      new(raw_data).attributes
    end

    def renamed_attributes
      @renamed_attributes ||= {}
    end

    def ignored_attributes
      @ignored_attributes ||= []
    end
  end

  def initialize(raw_data)
    @attributes = raw_data.each_with_object({}) do |(k, v), h|
      key = k.underscore.to_sym
      next if self.class.ignored_attributes.include?(key)

      attribute_name = self.class.renamed_attributes[key] || key 
      h[attribute_name] = v
    end
  end
end

# Can be defined for each model, or models can just use the default ModelTranslator
class ServiceTranslator
  include ModelTranslator

  rename :service_name, to: :service
  ignore :ignored_attribute
end

# Pretend this is an ActiveRecord class
class ServiceModel < OpenStruct
  attr_accessor :id, :name, :service
end

raw_data = ApiService.call

# When instantiating models, translation must be opted into by using the
# corresponding translator class.
model = ServiceModel.new(ServiceTranslator.call(raw_data))

puts model
# => #<ServiceModel id=1234, service="foo-bar", description="foo bar baz">