Rails response to CQRS

rails-response-to-cqrs.rb

# I have been recently exposed to Martin Fowler's CQRS concept and saw some implementations on .Net
# Like this http://www.codeproject.com/Articles/555855/Introduction-to-CQRS
# Disliked it as it brings a lot of noise in the code, a lot of handlers, class imbrications that defies simple human logic
# To say shortly, it's not quite cool, and as a rubyist I like keeping it simple and human
# Though the core concept of CQRS is quite simple, separate writes and reads to different database connections to increase global performance
# But implementation is very complex
# Lastly, someone I know even spent 2 years on a .Net project using CQRS (don't know how many weeks/months spend for just implementing the CQRS thing)
# I wrote this gist to see whether it can be done in 10 minutes
# And I did it in 10 minutes
# I love ActiveRecord so I DRYed by just extending it

# HEY This is just a concept

# TODO battle test it and improve it
# TODO make it as a gem
# TODO do the database sharding and replication stuffs to make your data consistent over different hosts
 
# NOTE This is open source so feel free to use, modify and share it if the concept interests you


# -----------------------------------
# PUT THE FOLLOWING IN AN INITIALIZER 
# -----------------------------------

module SwitchableConnection
  class ClassExtension
    def with_connection(connexion_array, &block)
      # randomly pick a connection
      # acting as a load balancer
      # connections are picked in a uniform way
      connexion = connexion_list[rand(connexion_array.length)]
      ActiveRecord::Base.establish_connection(connexion) unless ActiveRecord::Base.connection_config == connexion
      yield
    end
  end

  
  def with_connection(connexion_array, &block)
    self.class.with_connection(connexion_array, block)
  end


  def self.included(klass)
    klass.extend(ClassExtension)
  end
end

# Monkey patching ActiveRecord
# TODO move these connections configs into the config/database.yaml instead and load them from instead
module ActiveRecord
  class Base
    CONNECTIONS = {
      read: [
      {host: "any_host", adapter:"postgresql", encoding:"unicode", database:"db_name", pool: 5, username: "username", password:"xxxxxx"},
      {host: "any_host", adapter:"postgresql", encoding:"unicode", database:"db_name", pool: 5, username: "username", password:"xxxxxx"},
      {host: "any_host", adapter:"postgresql", encoding:"unicode", database:"db_name", pool: 5, username: "username", password:"xxxxxx"}
    ],

    write: [
      {host: "any_host", adapter:"postgresql", encoding:"unicode", database:"db_name", pool: 5, username: "username", password:"xxxxxx"},
      {host: "any_host", adapter:"postgresql", encoding:"unicode", database:"db_name", pool: 5, username: "username", password:"xxxxxx"},
      {host: "any_host", adapter:"postgresql", encoding:"unicode", database:"db_name", pool: 5, username: "username", password:"xxxxxx"}
    ]}

    CONNECTIONS.each do |mode, connexion_array|
      define_method "with_#{mode.to_s}_connection" do |&block|
        with_connection(connexion_array, block)
      end

      self.class.instance_eval do
        define_method "with_#{mode.to_s}_connection" do |&block|
          with_connection(connexion_array, block)
        end
      end
    end
  end
end


# -----------------------------------
# USAGE
# -----------------------------------

# In a model
class Customer < ActiveRecord::Base
  include SwitchableConnection

  def a_complex_operation_method
    # ....

    with_read_connection do

    end

    # ....

    with_write_connection do

    end

    # ....
  end
end

# In a controller
class AnyController < ApplicationController
  def any_action
    # ....

    Customer.with_read_connection do
      # any db reaching code ....
    end

    # ....

    Product.with_write_connection do
      # any db reaching code ....
    end

    # ....
  end
end

Here's the updated versions which is even lighter https://gist.github.com/FranckyU/9024949