gistfile1.rb

  module PersistentIdentityMap
    def self.included(base)
      base.extend(ResourceClassMethods)
    end
    
    def _dump(depth)
      marshaled_properties = properties.inject({}) do |h, p|
        h[p.instance_variable_name] = p.get!(self)
        h
      end
      Marshal.dump(marshaled_properties)
    end
  
    module ResourceClassMethods
      def _load(marshaled_properties)
        attributes = Marshal.load(marshaled_properties)
        resource = self.new
        resource.send(:properties).each do |p|
          p.set!(resource, attributes[p.instance_variable_name])
        end
        resource.instance_variable_set(:@saved, true)
        resource
      end
    end
  end

moneta_redis_identity_map.rb

require "moneta"
require 'moneta/redis'

module DataMapper
  # Tracks objects to help ensure that each object gets loaded only once.
  # See: http://www.martinfowler.com/eaaCatalog/identityMap.html
  class IdentityMap < Moneta::Redis
    extend Deprecate

    deprecate :get, :[]
    deprecate :set, :[]=
    
    def [](key)
      resource = super(key)
      Marshal.load(resource) if resource
    end
    
    def []=(key, resource)
      super(key, Marshal.dump(resource))
    end
    
  end # class IdentityMap
end # module DataMapper