rails-response-to-cqrs-2.rb

# V2, please see https://gist.github.com/FranckyU/9024250 for V1
# UPDATES
# - Monkey patching ActiveRecord::Base to to handle it all
# - The 'with_..._connection' methods get native without having to include any module


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

# Monkey patching ActiveRecord
# TODO move these connections configs into the config/database.yaml instead and load them from
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"}
    ]}

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

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

    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

  def a_complex_operation_method
    # ....

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

    # ....

    with_write_connection do
      # any db reaching code ....
    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

And why not making a convention to put those read/write blocks in database.yaml and refactor ActiveRecord usual methods like save, create, update_attributes, find etc to use those with_..._connection blocks automatically then abstracting the complex stuffs to the end user