to_hash.rb

# [:method_one, :method_two]
# [[:method_one, :other_method_one]]
# [[:method_one, :other_method_one, :other_method_two], :method_two]
# [{ :methodOne => :method_one, :methodTwo => :method_two }]
# [{ :methodOne => [:method_one, :other_method_one, :other_method_two], :methodTwo => :method_two }]
# [{ :methodOne => [:method_one, { :otherMethodOne => :other_method_one }], :methodTwo => :method_two }]

module ToHash
  def self.eval_object(object, attributes)
    if object.kind_of?(Array)
      object.map { |o| eval_attributes(o, attributes) }
    else
      eval_attributes(object, attributes)
    end
  end

  def self.eval_attributes(object, attributes)
    result = {}
    attributes = attributes.first if attributes.first.kind_of?(Hash)
    case attributes
    when Array
      attributes.each do |attribute|
        if attribute.kind_of?(Array)
          result[attribute.first] = eval_object(object.send(attribute.first), attribute[1..-1])
        else
          result[attribute] = object.send(attribute)
        end
      end
    when Hash
      attributes.each do |key, attribute|
        if attribute.kind_of?(Array)
          result[key] = eval_object(object.send(attribute.first), attribute[1..-1])
        else
          result[key] = object.send(attribute)
        end
      end
    end
    result
  end

  def to_hash(*attributes)
    ToHash.eval_attributes(self, attributes)
  end
end

require "ostruct"

project1 = OpenStruct.new(:title => "Project 1")
project2 = OpenStruct.new(:title => "Project 2")
project3 = OpenStruct.new(:title => "Project 3")

project1.authors = []
project1.authors << OpenStruct.new(:first_name => "John", :last_name => "Doe", :projects => [project1])
project1.authors << OpenStruct.new(:first_name => "Michael", :last_name => "Smith", :projects => [project1, project2])
project1.authors << OpenStruct.new(:first_name => "Jimmy", :last_name => "Parker", :projects => [project1, project2, project3])
project1.company = OpenStruct.new(:name => "HAL")

project1.extend(ToHash)

project1.to_hash(:title, [:authors, { :firstName => :first_name, :lastName => :last_name, :assignedProjects => [:projects, :title] }], [:company, :name])
#=> {:title=>"Project 1", :authors=>[{:firstName=>"John", :lastName=>"Doe", :assignedProjects=>[{:title=>"Project 1"}]}, {:firstName=>"Michael", :lastName=>"Smith", :assignedProjects=>[{:title=>"Project 1"}, {:title=>"Project 2"}]}, {:firstName=>"Jimmy", :lastName=>"Parker", :assignedProjects=>[{:title=>"Project 1"}, {:title=>"Project 2"}, {:title=>"Project 3"}]}], :company=>{:name=>"HAL"}}