test case for eager loading of nested associations with DataMapper

.gitignore

Gemfile.lock

dm_el.rb

#!/usr/bin/env ruby
# encoding: UTF-8

# test case for eager loading of nested associations with DataMapper

require 'rubygems'
require 'dm-core'
require 'dm-constraints'
require 'dm-migrations'
require File.expand_path('../eager_loading', __FILE__)

DataMapper::Logger.new($stdout, :debug)
DataMapper.setup(:default, "sqlite3://#{Dir.pwd}/db.sqlite")

class Person
  include DataMapper::Resource

  property :id, Serial
  property :name, String, :required => true

  has n, :vehicles

end

class Vehicle
  include DataMapper::Resource

  property :id, Serial
  property :name, String, :required => true

  has n, :components

end

class Component
  include DataMapper::Resource

  property :id, Serial
  property :name, String, :required => true

  belongs_to :manufacturer

end

class Manufacturer
  include DataMapper::Resource

  property :id, Serial
  property :name, String, :required => true

end

DataMapper.auto_migrate!

# generate test data

Person.create(:name => "FND", :vehicles => [
  Vehicle.create(:name => "Taurus", :components => [
    Component.create(:name => "engine",
        :manufacturer => Manufacturer.create(:name => "Ford")),
    Component.create(:name => "radio",
        :manufacturer => Manufacturer.create(:name => "Bose"))
  ]),
  Vehicle.create(:name => "fixie", :components => [
    Component.create(:name => "frame",
        :manufacturer => Manufacturer.create(:name => "Campagnolo")),
    Component.create(:name => "breaks",
        :manufacturer => Manufacturer.create(:name => "Shimano"))
  ])
])

Person.create(:name => "tillsc", :vehicles => [
  Vehicle.create(:name => "Golf", :components => [
    Component.create(:name => "engine",
        :manufacturer => Manufacturer.create(:name => "VW"))
  ])
])

# retrieve data

puts "", "[INFO] test case A"
person = Person.get!(1)
puts person.vehicles.components.manufacturer.map(&:name).join(", ")

puts "", "[INFO] test case B"
people = Person.all
people.each do |person|
  person.vehicles.each do |vehicle|
    puts sprintf("%-10s %-10s", person.name, vehicle.name)
  end
end

puts "", "[INFO] test case C    ===== /!\ n+1 hazard ===="
people = Person.all
people.each do |person|
  person.vehicles.each do |vehicle|
    vehicle.components.each do |component|
      puts sprintf("%-10s %-10s %-10s", person.name, vehicle.name, component.name)
    end
  end
end

puts "", "[INFO] test case D"
people = Person.all
people.eager_load(Person.vehicles.components).each do |person|
  person.vehicles.each do |vehicle|
    vehicle.components.each do |component|
      puts sprintf("%-10s %-10s %-10s", person.name, vehicle.name, component.name)
    end
  end
end

eager_loading.rb

# manual eager loading for DataMapper
module EagerLoading

  def eager_load(query_path)
    query_path.relationships.inject(self) do |collection, relationship|
      relationship.eager_load(collection)
    end

    self
  end

end

DataMapper::Collection.send(:include, EagerLoading)

Gemfile

source :rubygems

DM_VERSION    = '~> 1.2.0.rc2'

gem 'dm-core', DM_VERSION
gem 'dm-constraints', DM_VERSION
gem 'dm-migrations', DM_VERSION
gem 'dm-sqlite-adapter', DM_VERSION

run.sh

#!/usr/bin/env sh

rm db.sqlite

# reformat SQL queries for readability
bundle exec ./dm_el.rb | perl -pe 's#SELECT .*? (FROM ".*?" )(.*)#\1SELECT ... \2#'

This looks like a promising start in the right direction. For some reason it looks like it's not loading components. It should have FROM "components" SELECT ... WHERE "vehicle_id" IN (1, 2, 3) ORDER BY "id" and not have that final select ;) I'm not too sure why it comes out that way, but DM out of the box produces that output, which struck me as a little odd.

Apologies for not chiming into the other gist last night. I was busy working on some work-related stuff :) Will have another play with this later.