Transformers is an extension to hash to allow various transformations using simple DSL. It also has optional rails extension to dry up frequently applied transformations on controller params.

    gem install transformers

OR Add dependency in Gemfile for projects using bundler

    gem 'transformers'

• Convert values

    hash = {:foo => 'bar'}
  
    hash.convert :eric, :to => lambda { |value| value.upcase }
  
  OR use short hand notation to call a method on the value
  
    hash.convert :foo, :to => :upcase
  

• Combine keys

    hash.convert :begin, :end, :as => :range
  

• Rename keys

    hash.rename :foo, :to => :bar
  
  OR
  
    hash.convert :foo, :as => :bar
  

• Alias key

    hash.copy :foo, :to => :bar
  

• Convert and combine

    hash.convert :first_name, :last_name, :as => :name, :to => lambda { |first_name, last_name| first_name + ' '+ last_name }
  

• Conversion using type converters

    hash = {:foo => 'true'}
  
    hash.convert :foo, :to => :boolean         #built-in
  

• Using Custom converters : You can pass a lambda or define a module or an object which has a call method. This method will receive values for given keys and should return the converted value.

    module Transformers::Name
      def self.call(first_name, last_name)
        return first_name + ' '+ last_name
      end
    end
  

  Register the converter

    Transformers.register(:name, Transformers::Name)
  

  Usage

    hash.convert :first_name, :last_name, :as => :name, :to => :name
  

• Use them together in a transform block

    hash.transform do
      delete :unwanted
      rename :foo, :to => :bar
      convert :first_name, :last_name, :as => :name, :to => :name
    end
  

To Include rails extensions add the below line in a config/initializer/transformers.rb. You can register the custom transformers in the same file.

    require 'transformers/rails'

This adds transform_params extension to action controller. You can define the transformations for any action as,

    transform_params :search, :only => :index do
      convert :first_name, :last_name, :as => :name, :to => :name
    end

This will add a before_filter in the controller to apply transformations on params[:search]. If the first argument is omitted, the transformations will be applied directly on the params. The options for transform_params are same as before_filter options.

This gem has a rspec matcher for testing the custom converters. To use this, add the below line in the spec_helper

    require 'rspec/transformers'

The converter spec can be written as

    describe Transformers::Boolean do
      it { should convert('true').to(true)}
      it { should convert('false').to(false)}
    end