benchmark_preload_has_many_through.rb

require 'benchmark/ips'

begin
  class CreateModels < ActiveRecord::Migration
    def change
      create_table :items do |t|
      end

      create_table :events do |t|
        t.belongs_to :item
      end

      create_table :event_people do |t|
        t.belongs_to :event
        t.belongs_to :person
      end

      create_table :people do |t|
      end
    end
  end

  class Item < ActiveRecord::Base
    has_many :events
    has_many :event_people, :through => :events
    has_many :people, :through => :events
  end

  class Event < ActiveRecord::Base
    belongs_to :item
    has_many :event_people
    has_many :people, :through => :event_people
  end

  class EventPerson < ActiveRecord::Base
    belongs_to :event
    belongs_to :person
  end

  class Person < ActiveRecord::Base
  end

  ActiveRecord::Migration.verbose = false
  CreateModels.new.change

rescue => e
  # Tables already exist
  # puts e.message
end

unless Item.count >= 100
  puts "Populating Database"
  1000.times do
    Item.create
  end

  Item.all.each_with_index do |item|
    event = Event.new
    event.people.build
    event.people.build
    item.events << event
  end
end

puts "=" * 80
puts "Benchmark : Preload has_many_through association"
puts "#{Rails.version} - #{ActiveRecord::Base.configurations[Rails.env]['adapter']}"
puts "=" * 80
puts ""

Benchmark.ips do |x|
  x.report('limit 100 has_many') { Item.preload(:events).limit(100).order(:id).to_a }
  x.report('limit 100 has_many_through') { Item.preload(:event_people).limit(100).order(:id).to_a }
  x.report('limit 100 double has_many_through') { Item.preload(:people).limit(100).order(:id).to_a }
  x.report('limit 1000 has_many') { Item.preload(:events).limit(1000).order(:id).to_a }
  x.report('limit 1000 has_many_through') { Item.preload(:event_people).limit(1000).order(:id).to_a  }
  x.report('limit 1000 double has_many_through') { Item.preload(:people).limit(1000).order(:id).to_a  }
end