roar.rb

require "roar/coercion"
require "roar/json/hal"
require "json"

module CategoryRepresenter
  include Roar::JSON::HAL
  include Roar::Hypermedia
  include Roar::Coercion

  property :name
end

class Category
  include Roar::JSON
  include CategoryRepresenter

  attr_accessor :name
end

module PostRepresenter
  include Roar::JSON::HAL
  include Roar::Hypermedia
  include Roar::Coercion

  property :name

  property :category, class: Category do
    property :name
  end
end

class Post
  include Roar::JSON
  include PostRepresenter

  attr_accessor :name, :category
end

module CollectionRepresenter
  include Roar::JSON::HAL
  include Roar::Hypermedia
  include Roar::Coercion

  property :name

  property :post, class: Post do
    property :name
  end
end

class Collection
  include Roar::JSON
  include CollectionRepresenter

  attr_accessor :post
end


post_hash = JSON.load('{"name":"post","category":{"name":"cat"}}')
post = Post.new.from_hash(post_hash)

puts post_hash["category"]["name"]
# => cat

puts post.category.name
# => cat


col_hash = JSON.load('{"post":{"name":"post","category":{"name":"cat"}}}')
col = Collection.new.from_hash(col_hash)

puts col_hash["post"]["category"]["name"]
# => cat

puts col.post.category.name
# => NoMethodError