Mapper generator using Virtus model

example.rb

class User
  include DataMapper::Model

  attribute :id,   Integer
  attribute :name, String
  attribute :age,  Integer
end

DataMapper.generate_mapper_for(User) do
  key :id
  rename :name => :username
end

DataMapper.finalize

virtus_mapper_generator_spike.rb

module DataMapper
  class Mapper::Relation::Base < Mapper::Relation

    def self.configure(&block)
      instance_exec(&block)
      finalize
    end
  end

  module Model
    def self.included(model)
      model.send(:include, Virtus)
    end
  end

  def self.generate_mapper_for(model, &block)
    mapper = Class.new(Mapper::Relation::Base)
    mapper.model(model)
    mapper.relation_name(Inflector.tableize(model.name))
    mapper.repository :postgres

    mapper.instance_exec(&block)

    model.attribute_set.each do |attribute|
      next if mapper.attributes[attribute.name]
      mapper.map attribute.name, attribute.options[:primitive]
    end

    mapper.class_eval do
      def self.name
        "#{model.name}Mapper"
      end

      def self.inspect
        "<##{name}:#{object_id}>"
      end
    end

    mapper
  end
end