Integer sequence ids in Mongo

sequence.rb

require 'rubygems'
require 'mongoid'

Mongoid.configure do |config|
  config.master = Mongo::Connection.new.db("test")
end

Mongoid.database.add_stored_function 'sequence', <<-__

  function(sequence) {
    var doc =
      db.sequences.findAndModify({
        'query'  : {_id  : sequence},
        'update' : {$inc : {'value' : 1}},
        'new'    : true,
        'upsert' : true
      });

    return doc.value;
  }

__

module Mongoid
  class Sequence
    include Mongoid::Fields::Serializable

    def Sequence.for(name)
      sequence = new
      sequence.name = name.to_s
      sequence
    end

    attr_accessor(:name)

    def instantiate(*args)
      self
    end

    def deserialize(object)
      object.to_i
    end

    def serialize(object)
      case object
        when false, nil
          Mongoid.master.eval("sequence('#{ name }')").to_i
        when BSON::ObjectId
          object.to_s.to_i(16)
        when Integer
          object
        else
          Integer(object)
      end
    end
  end

  module Document
    module ClassMethods
      def sequence
        @sequence ||= Sequence.for(collection.name)
      end
    end
  end
end


class B
  include Mongoid::Document
end


class A
  include Mongoid::Document

  A.field(:_type, :type => String, :default => name)

  A.field(:_id, :type => sequence, :default => nil)

  if respond_to?(:identity)
    identity(:type => String, :default => proc{ generate_id }) rescue nil
  end

  if respond_to?(:using_object_ids)
    self.using_object_ids = false
  end

  ::Mongoid::Identity.class_eval do
    def generate_id
      @document.respond_to?(:generate_id) ? @document.generate_id : BSON::ObjectId.new
    end
  end

  def self.generate_id
    nil
  end

  def generate_id
    self.class.generate_id
  end
end





require 'benchmark'

B.delete_all
A.delete_all

n = 10_000

Benchmark.bm do |bm|
  bm.report('B'){ n.times{ B.create } }
  bm.report('A'){ n.times{ A.create } }
end


__END__

       user     system      total        real
       B  2.450000   0.140000   2.590000 (  2.595748)
       A  4.320000   0.460000   4.780000 (  8.151828)