An example "orm" for redis.

invitation.rb

class Invitation < RedisDataMapper

  key_property :mail
  key_property :type

  key_format -> { |attrs| "invitation:#{attrs[:type]}#{attrs[:mail]}" }

  property :token
  property :mail_sent
  property :accepted

  scope :all, 'invitation:*'
  scope :admin, 'invitation:admin:*'
end

redis_data_mapper.rb

class RedisDataMapper
  attr_accessor :key_attributes

  def initialize(key_attributes = {})
    @key_attributes = {}
    self.class.key_property_list.each do |key|
      if key_attributes[key]
        @key_attributes[key] = key_attributes[key]
      else
        fail ArgumentError, "Missing key attribute #{key}"
      end
    end
  end

  def connection
    @connection || REDIS
  end

  def reload
    @properties = {}
    @dirty_properties = {}
  end

  def update(attrs)
    @dirty_properties.merge!(attrs)
    save
  end

  def save
    @dirty_properties.each do |sub_key, value|
      connection.hset(key, sub_key, value)
      properties[sub_key] = value
    end
    @dirty_properties = {}
    true
  end

  def key
    @key ||= self.class.key_format.call(key_attributes)
  end

  def properties
    @properties ||= {}
  end

  def dirty_properties
    @dirty_properties ||= {}
  end

  class <<self
    attr_accessor :key_format

    def key_format(proc)
      @key_format = proc
    end

    def key_property(name)
      key_property_list << name
      define_method(name) do
        key_property[name]
      end
    end

    def scope(name, key)
      define_class_method(name) do
        map_results(REDIS.keys(key))
      end
    end

    def map_results(results)
      results.map(&:new)
    end

    def property(name)
      property_list << name

      define_method(name) do
        properties[sub_key] ||= connection.hget(key, name)
      end

      define_method("#{name}=") do |value|
        dirty_properties[name] = value if value != __send__(name)
      end
    end

    def property_list
      @property_list ||= []
    end

    def key_property_list
      @key_property_list ||= []
    end
  end
end

redis_orm_example.rb

i = Invitation.new(type: 'admin', email: 'pippo')
i.mail_sent = true
i.save