Gemfile

source :rubygems

gem 'pg'
gem 'activesupport'

gem "debugger"

# DM2 staff
gem 'dm-mapper', git: "https://github.com/solnic/dm-mapper.git"

gem 'veritas', git: 'https://github.com/solnic/veritas.git'
gem 'veritas-sql-generator', git: 'https://github.com/solnic/veritas-sql-generator.git', branch: "string-concat-function-support"
gem 'veritas-optimizer', git: 'https://github.com/dkubb/veritas-optimizer.git'
gem 'veritas-do-adapter', git: 'https://github.com/dkubb/veritas-do-adapter.git'
gem 'virtus', git: 'https://github.com/solnic/virtus.git'
gem 'do_postgres'

test.rb

require 'bundler/setup'
Bundler.require :default
require 'veritas'
require 'veritas/optimizer'
require 'veritas-do-adapter'
require 'virtus'
require 'do_postgres'

require 'dm-mapper'

require 'debugger'

url = "postgres://rails:rails@localhost:5432/ar_dm2"

DataMapper.setup(:postgres, url)
DataObjects.logger.set_log('do.log', :debug)
connection = DataObjects::Connection.new(url)

connection.create_command(<<-SQL).execute_non_query
DROP TABLE IF EXISTS "public"."users";
DROP SEQUENCE IF EXISTS "users_id_seq";

CREATE SEQUENCE "users_id_seq" INCREMENT 1 START 1 MAXVALUE 9223372036854775807 MINVALUE 1 CACHE 1;
ALTER TABLE "users_id_seq" OWNER TO "rails";

CREATE TABLE "public"."users" (
	"id" int4 NOT NULL DEFAULT  nextval('users_id_seq'::regclass),
	"name" varchar(255) NOT NULL
)
WITH (OIDS=FALSE);
ALTER TABLE "public"."users" OWNER TO "rails";

insert into "public"."users" ( "name") values ( 'octocat');
insert into "public"."users" ( "name") values ( 'dhh');
SQL

  class User
    attr_accessor :likes, :id, :name

    def initialize(attributes={})
      @id = attributes[:id]
      @name = attributes[:name]
      @likes = attributes[:likes]
    end
  end

  class Mapper < DataMapper::Mapper::VeritasMapper
    map :id,   to: :id,   :type => Integer
    map :name,   to: :name,   :type => String

    model         User
    relation_name :users
    repository    :postgres
  end


  DataMapper.finalize

  profiles_json   = [
    {"profile"=>{"user_id"=>1, "likes"=>"meat, kats"}},
    {"profile"=>{"user_id"=>2, "likes"=>"ruby, mac"}},
    {"profile"=>{"user_id"=>3, "likes"=>"be invisible"}}
  ]

  profiles_header = [
    [:user_id, Integer],
    [:likes,   String ]
  ]
  profiles_tuple = profiles_json.map do |profile|
    [ profile['profile']['user_id'], profile['profile']['likes']]
  end
  profiles_relation = Veritas::Relation::Base.new('profiles', profiles_header, profiles_tuple)


  puts "Example from gist"

  adapter = Veritas::Adapter::DataObjects.new(url)
  users_header = [ [ :id, Integer ], [ :name, String ] ]

  user_alt_relation = Veritas::Relation::Gateway.new(
    adapter, Veritas::Relation::Base.new('users', users_header))

  new_alt_relation = user_alt_relation.join(profiles_relation) do |r|
    r.id.eq(r.user_id)
  end

  new_alt_relation.each do |user|
    puts "User #{user[:id]} named #{user[:name]} likes #{user[:likes]}"
  end

  puts "Use Ruby object"

  user_relation = DataMapper[User]

  new_relation = user_relation.join(profiles_relation) do |r|
    puts "Joining id=#{r.id} and user_id=#{r.user_id}"
    r.id.eq(r.user_id)
  end

  new_relation.each do |user|
    puts "User #{user.id} named #{user.name} likes #{user.likes}"
  end