Example of embeding model in ActiveRecord using JSON and postgreSQL

console.sh

2.1.1 :052 > t = Test.new()
 => #<Test id: nil, data: nil, created_at: nil, updated_at: nil>
2.1.1 :053 > t.virt = Virt.new(address: { street: 'pięknie jest', nr: 5 })
 => #<Virt:0x00000106100458 @address={:street=>"pięknie jest", :nr=>5}, @name=nil, @children=[]>
2.1.1 :054 > t.save!
   (0.4ms)  BEGIN
  SQL (0.4ms)  INSERT INTO "tests" ("created_at", "data", "updated_at") VALUES ($1, $2, $3) RETURNING "id"  [["created_at", "2014-10-07 21:56:49.991978"], ["data", "{\"name\":null,\"address\":{\"street\":\"pięknie jest\",\"nr\":5},\"children\":[]}"], ["updated_at", "2014-10-07 21:56:49.991978"]]
   (2.0ms)  COMMIT
 => true
2.1.1 :055 > t.reload
  Test Load (0.4ms)  SELECT  "tests".* FROM "tests"  WHERE "tests"."id" = $1 LIMIT 1  [["id", 10004]]
 => #<Test id: 10004, data: {"name"=>nil, "address"=>{"street"=>"pięknie jest", "nr"=>5}, "children"=>[]}, created_at: "2014-10-07 21:56:49", updated_at: "2014-10-07 21:56:49">
2.1.1 :056 > t.virt
 => #<Virt:0x00000106119fc0 @address={"street"=>"pięknie jest", "nr"=>5}, @name=nil, @children=[]>
2.1.1 :057 > t.virt.address
 => {"street"=>"pięknie jest", "nr"=>5}
2.1.1 :058 > t.virt.address.class
 => Hash
2.1.1 :059 > t.virt.class
 => Virt
2.1.1 :060 > t.virt.parent == t
 => true
2.1.1 :061 > t.virt.parent.virt == t.virt
 => true

create_tests.rb

class CreateTests < ActiveRecord::Migration
  def change
    create_table :tests do |t|
      t.json :data

      t.timestamps
    end
  end
end

embedded_model.rb

 module EmbeddedModel

   def embeds_one(name, options)
     column_name = options.fetch(:column_name, nil) || name
     define_method("#{name}=") do |arg|
       write_attribute(column_name, arg.is_a?(Hash) ? arg : arg.to_h)
     end

     define_method(name) do
      if instance_variable_get("@#{name}").nil?
       model = name.to_s.classify.constantize.new(read_attribute(column_name))
       inverse_of = options.fetch(:inverse_of, nil) || self.class.name.downcase
       model.public_send("#{inverse_of}=", self)
       instance_variable_set("@#{name}", model)
      end
      instance_variable_get("@#{name}")

     end
   end
   
   def embedded_in(name, options = {})
    klass_name = options.fetch(:class_name, nil) || name.classify
    self.attribute name, klass_name.to_s.constantize
  end

 end

test.rb

class Test < ActiveRecord::Base
  extend EmbeddedModel

  embeds_one :virt, column_name: :data, inverse_of: :parent
end

virt.rb

class Virt
  include Virtus.model

  attribute :name, String
  attribute :address, Hash
  attribute :children, Array
  
  embedded_in :parent, class_name: Test
  
end