vsavkin

blog = Blog.create
post = blog.make_post text: 'great post', location_country: 'Canada', location_city: 'Toronto'
post.make_comment text: 'great comment', location_country: 'Canada', location_city: 'Toronto'

vsavkin

class Blog < ActiveRecord::Base
  ...

  def all_posts_from country, city
    ...
  end

  def all_comments_from country, city
    ...
  end

vsavkin

class LocationPresenter
  def initialize country, city
    ...
  end
end

vsavkin

class Location < Struct.new(:country, :city)
end

vsavkin

class Post < ActiveRecord::Base
  composed_of :location, mapping: [%w(location_country country),
                                   %w(location_city city)]

  def self.all_posts_from location
    Post.where location: location
  end
end

vsavkin

blog.make_post text: 'great post 2', location: Location.new('Canada', 'Toronto')

vsavkin

def Toronto
  Location.new('Canada', 'Toronto')
end

...

blog.make_post text: 'great post', location: Toronto

vsavkin

class Location < ActiveRecord::Base
  validates :city, :uniqueness => {:scope => :country}

  def self.get country, city
    location = Location.find_by_country_and_city(country, city)
    raise "There is no '#{city}' in '#{country}'" unless location
    location.readonly!
    location
  end

vsavkin

toronto = Location.get('Canada', 'Toronto')
blog.make_post text: 'great post 2', location: toronto

vsavkin

# The User class has two attributes: name and age.

# STEP 1: Call restrict_ar! inside your model definition. It will make most AR methods private.

class User < ActiveRecord::Base
  restrict_ar!
end

# All AR class methods will become private. As a result, the following calls will raise an exception:
User.create! # BOOM