redis_map.rb

    class RedisMap
      def initialize(redis)
        @redis = redis
      end

      def clear
        redis.del key
        fail 'failed to delete' if redis.exists key
      end

      def all(klass)
        read.all klass
      end

      def get(klass, id)
        read.get klass, id
      end

      def set(record)
        map = read
        map.set record
        write map
      end

      def delete(record)
        map = read
        map.delete record
        write map
      end

      private
      def key
        'repo'
      end

      def redis
        @redis
      end

      def read
        value = redis.get key
        value ? YAML.load(value) : RecordMap.new
      end

      def write(map)
        redis.set key, YAML.dump(map)
      end
    end