mongo_test.rb

require 'mongo'
require 'mongo_record'
require 'memcached'

MongoRecord::Base.connection =
  Mongo::Connection.new("75.101.206.153").db('trader_network_trois')

$cache = Memcached.new("localhost:11211")

class ItemOfInterest < MongoRecord::Base
  collection_name :items_of_interest
  fields :type, :id, :json, :interested
end

class Interest < MongoRecord::Subobject
  fields :member_id, :cause, :cause_type, :cause_id
end

class MongoTest

  def self.cache_key(type, id)
    [type, id].join(":")
  end
    
  ...
end

trade = Trade.find(5187411)
items = trade.distributions
RAILS_DEFAULT_LOGGER.info("Distributing item to #{items.size} members")
items.each_with_index do |afi, iteration|
  key_hash = {:type => afi.real_item_type, :id => afi.item_of_interest_id}
  ioi = ItemOfInterest.find(:first, :conditions => key_hash)
  RAILS_DEFAULT_LOGGER.info("Iteration #{iteration}: Interested size (at load): #{ioi.interested.size}") if ioi
  unless ioi
    ioi = ItemOfInterest.new(key_hash)
    begin
      ioi.json = $cache.get(MongoTest.cache_key(afi.item_of_interest_type, afi.item_of_interest_id))
    rescue Memcached::NotFound
      ioi.json = afi.item_of_interest.to_json
      $cache.set(MongoTest.cache_key(afi.item_of_interest_type, afi.item_of_interest_id),ioi.json)
    end
    ioi.interested = []
  end
  begin
    cause_json = $cache.get(MongoTest.cache_key(afi.cause_type, afi.cause_id))
  rescue Memcached::NotFound
    cause_json = afi.cause.to_json
    $cache.set(MongoTest.cache_key(afi.cause_type, afi.cause_id),cause_json)
  end
  RAILS_DEFAULT_LOGGER.info("Iteration #{iteration}: Interested size (before append): #{ioi.interested.size}")
  ioi.interested << Interest.new(:member_id => afi.member_id, :cause => cause_json,
                                  :cause_type => afi.real_cause_type, :cause_id => afi.cause_id)
  RAILS_DEFAULT_LOGGER.info("Iteration #{iteration}: Interested size (after append): #{ioi.interested.size}")
  ioi.save
  RAILS_DEFAULT_LOGGER.info("Iteration #{iteration}: Interested size (after save): #{ioi.interested.size}")  
end

staging.log

Iteration 0: Interested size (before append): 0
Iteration 0: Interested size (after append): 1
Iteration 0: Interested size (after save): 1
Iteration 1: Interested size (at load): 1
Iteration 1: Interested size (before append): 1
Iteration 1: Interested size (after append): 2
Iteration 1: Interested size (after save): 2
Iteration 2: Interested size (at load): 1
Iteration 2: Interested size (before append): 1
Iteration 2: Interested size (after append): 2
Iteration 2: Interested size (after save): 2
Iteration 3: Interested size (at load): 1
Iteration 3: Interested size (before append): 1
Iteration 3: Interested size (after append): 2
Iteration 3: Interested size (after save): 2