traverse_associations.rb

def traverse instance
  attributes = instance.attributes
  klass      = instance.class

  associations = klass.reflect_on_all_associations

  return attributes unless associations

  associations.map(&:name).each do |key|
    result = instance.send key
    value  = nil

    value = if result
      association = klass.reflect_on_association key

      case association.macro
      when :has_many then result.map { |o| call o }
      when :has_one  then call result
      end
    end

    attributes.merge! key.to_s => value
  end

  attributes
end