Separating model from ActiveRecord with delegation/decorator pattern.

forwardable.rb

require "forwardable"

module ActiveRecord

  class Base

    def save
      puts "SAVED #{name}"
    end

  end

end

class Person

  attr_reader :name

  def initialize(name)
    @name = name
  end

end

class PersonRecord < ActiveRecord::Base

  extend Forwardable

  def_delegators :@person, :name

  def initialize(person)
    @person = person
  end

end

p = Person.new("John Doe")
pr = PersonRecord.new(p)
pr.save

method_missing + forwardable.rb

require "forwardable"

# fake AR implementation

module ActiveRecord

  class Base

    def save
      puts instance_variables.collect { |var| "#{var}: #{instance_variable_get(var)}" }
    end

  end

end

# Generic wrapper for AR records

class Record < ActiveRecord::Base

  def initialize(target)
    @target = target
  end
  
  attr_reader :target

  # avoid having to explicitly delegate everything
  def method_missing(method_name, *args, &block)
    @target.respond_to?(method_name) ? @target.send(method_name, *args, &block) : super
  end

  # bonus: explicit delegation of metaprogramming features
  extend Forwardable
  delegate [:instance_variables, :instance_variable_get, :instance_variable_set] => :@target

end

# model class

class Person

  # may include ActiveModel stuff here

  attr_reader :name

  def initialize(name)
    @name = name
  end

end

# record class

class PersonRecord < Record

  # only AR stuff (e.g. relations)

end

p = Person.new("John Doe")
pr = PersonRecord.new(p)
pr.save