I was spiking on Redis recently. I wanted to use the redis-objects gem to simulate a shopping cart app even though the README specifically says

Just use MySQL, k?

I wanted to see what would happen if I tried it anyway. So the README and examples for the redis-objects gem are great so I’m not going to rehash what’s there. However, I will say though that the example has you hardcode the id field to 1. That detail snuck up on me.

If you don’t set an ID then you can’t work with a redis-object instance. You get an exception: Redis::Objects::NilObjectId: Attempt to address redis-object :name on class User with nil id (unsaved record?)

It’s basically trying to tell you, “hey, save the record first or set an ID”. Well, honestly, I don’t want to set an id myself. This is where the meat of the README is. Redis-objects really fits organically in an existing ActiveRecord model. That means Rails. In this case though, I don’t want an entire Rails app. I can see the value though in a plain old Rails app. Just look at the examples if you want to see more.

Anyway, continuing on with the spiking, I tried to integrate the Supermodel gem with Redis-objects. That sort of worked. You just class User < Supermodel::Base and you can sort of get it to work. This is great because Supermodel gives you finders like User.find_by_email('bob@yahoo.com') to make it act like ActiveRecord but you can’t use .create(email: 'bob@yahoo.com') to begin with because of the same errors as I mentioned above. Redis-objects really wants the record to have an ID already. Even using Supermodel’s RandomID mixin didn’t work. The initialize order and callback hooks don’t really work (or at least I couldn’t get them to work).

Finally, I tried combining just redis-objects and datamapper redis. That worked. And it’s pretty nice. Check it out.

require 'redis-objects'
require 'dm-core'
require 'dm-redis-adapter'

DataMapper.setup(:default, {:adapter  => "redis"})

# you would move this to a common location
Redis.current = Redis.new(:host => '', :port => 6379)

class User
  include Redis::Objects
  include DataMapper::Resource

  # datamapper fields, just used for .create
  property :id, Serial
  property :email, String

  # use redis-objects fields for everything else
  value :disabled
  value :name
  list :cart, :marshal => true


# absolutely need this line for dm-redis

So using this is pretty easy.

u = User.create(email: 'test@test.com')
u.name = 'Testy McTesterson'

When you look at Redis, the keys are already composited for you and magic has happened.

redis> keys *

redis> get user:test@test.com:name
Testy McTesterson


The name field is from redis-objects and the create uses datamapper. This is a really odd pairing but I like the fact that I have no sql database in the mix but still have finders similar to an ORM. Something to keep in mind, datamapper’s finders are a bit different than the Rails 3 ones (no .where method).

Benchmarking A Million Things

Ok fine. So maybe this works, maybe it doesn’t. Maybe it’s not the right idea. What about the good stuff? Like, how fast can we load a whole lot of names into MySQL versus Redis using the above code and techniques? Is it even relevant?

(PL = pipelined redis operation)

Loading one million random names (full names) like John Smith, Patty Gerbee Sr)
MySQL:                   06:05
Redis:                   02:45
Redis C ext              01:32
Redis pipelined:         00:56
Redis pipelined C ext:   00:19
Ruby just loading array: 387ms

Loading 10k ecommerce-style data (orders, users, products)
MySQL:    00:09.40
Redis:    00:14.50
Redis PL: 00:02.72

A gist of these test results is here.

A More Complete Example

If you know the ID and don’t need something like an auto-incrementing column outside your code/control then you can greatly simplify the code above by getting rid of Datamapper. You can simply use redis-objects to fake an ORM. I had great success using it as long as you USE NATIVE REDIS TYPES. Listen to the redis-objects author, don’t try to force the tool into the use case.

# What if we want to use redis-objects as a database but
# try to stick with native redis objects?
# For example, Supermodel is a great gem but using the Redis
# mixin causes Supermodel to serialize to JSON strings in Redis
# which is going to kill performance.  You have to model your
# problem using native Redis objects to keep the speed up.
# At the same time, I miss the finders from ActiveModel
# like: Person.find('Joe')
# Supermodel does give you those finders so you will feel right at
# home coming from Rails.  I tried using ActiveModel mixins with
# redis-objects but it didn't work for me.
# I found the below a nice compromise but it requires a lot of
# custom methods.  :(

require 'redis-objects'

class Person
  attr_reader :name
  alias :id :name

  include Redis::Objects

  def initialize name
    @name = name

  def self.exists? name
    # Here's a big assumption, if the id attribute exists, the entire
    # object exists.  This might not work for your problem.
    self.redis.exists "name:{#name}:id"

  def self.find name
    # new behaves like find when a record exists, so this works like
    # find_or_create()
    self.new name

  # native redis attributes with redis-objects
  value :age
  list :favorite_foods

# example usage

joe = Person.new 'Joe'
joe.age = 34
joe.favorite_foods << ['cake', 'pie']  # it will flatten arrays, don't worry
joe.favorite_foods << 'bacon'          # or you can do this

Person.find('Joe').age = 56

# find and initialize
Person.find('Stan').age = 21

# you cannot just .favorite_foods = ['Steak]' because that's not how native
# Redis objects work
Person.find('Stan').favorite_foods << 'Steak'

# deleting a field
Person.find('Stan').favorite_foods.del  # notice it's .del and not .delete (del is the redis cmd)


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