Redis: WATCH use case

watch.rb

require "redis"
R = Redis.new

def watching(*kk)
  5.times do
    R::watch(*kk)
    begin
      r = yield
    rescue Object => e
      R::unwatch
      raise e
    end
    return r unless r.nil?
    sleep 1
end
  raise("Error watching #{kk.inspect}")
end

# create user "daniel"
R::hmset("u:23","name","daniel","email","daniel@example.com")
# change schema (u -> users)
watching("u:23") do
  n,e = R::hmget("u:23","name","email")
  R::multi{ R::hmset("users:daniel","name",n,"email",e) }
end

# "daniel" can change his email in the meantime!