eager_loading_test.rb

require 'dm-core'
require 'dm-sweatshop'
require 'dm-migrations'

class Foo
  include DataMapper::Resource
  
  property :id, Serial
  property :name, String
  property :sku, String
end

DataMapper::Logger.new($stdout, :debug)
DataMapper.setup(:default, "mysql://localhost/test")
DataMapper.auto_migrate!

Foo.fix{{ :name => /\w+( \w+){0,2}/.gen, :sku => /\w+( \w+){0,2}/.gen}}
10.of{Foo.gen}

Foo.all.each{ |f| puts f.sku }

class Bar
  include DataMapper::Resource
  
  property :id, Serial
  property :name, String
  property :sku, String
  
  belongs_to :foo
end

Foo.has(1.0/0, :bars)
Bar.auto_migrate!

Bar.fix{{ :name => /\w+( \w+){0,2}/.gen, :sku => /\w+( \w+){0,2}/.gen, :foo => Foo.pick}}
10.of{ Bar.gen }

Foo.all.map{ |f| f.bars.first }.size == Bar.all.map(&:foo_id).uniq.size

Foo.all.map{ |f| f.bars.first } # => SELECT `id`, `name`, `sku`, `foo_id` FROM `bars` WHERE `foo_id` IN (1, 2, 3, 4, 5, 6, 7, 8, 9, 10) ORDER BY `id`

__END__
ruby-1.9.2-p0 :053 > Foo.all.map{ |f| b = f.bars.first; b.name if b  }
 ~ (0.000202) SELECT `id`, `name`, `sku` FROM `foos` ORDER BY `id`
 ~ (0.007954) SELECT `id`, `name`, `sku`, `foo_id` FROM `bars` WHERE `foo_id` IN (1, 2, 3, 4, 5, 6, 7, 8, 9, 10) ORDER BY `id`
 => [nil, "semipreservation oppositive", "tossment beguileful morologically", "unsolicitously oxyrhine agrarian", "hummeler fibromyotomy fiendly", nil, nil, "proustite delible", nil, "complimentingly kochliarion"]