nest of ActiveModel::Serializers::JSON (rails5)

serializer_json.rb

class Bar
  include ActiveModel::Model

  attr_accessor :foo, :bar
end

class Foo
  include ActiveModel::Model
  include ActiveModel::Serializers::JSON

  attr_accessor :foo, :bar
  def attributes=(hash)
    @foo = hash["foo"]
    @bar = Bar.new(hash["bar"])
  end

  def attributes
    {foo: @foo, bar: @bar}
  end
end

class Hoge
  include ActiveModel::Model
  include ActiveModel::Serializers::JSON

  attr_accessor :foo, :bar
  def attributes=(hash)
    @foo = Foo.new.from_json(hash["foo"].to_json)
    @bar = hash["bar"]
  end

  def attributes
    {foo: @foo, bar: @bar}
  end
end

a = Hoge.new(foo: Foo.new(foo: 234, bar: Bar.new(foo: 345, bar: 456)), bar: 123)

pp a
j = a.to_json
puts s
pp JSON.parse(j)

puts '----------------------------'

b = Hoge.new.from_json(j)
pp b
pp b.to_json
pp JSON.parse(b.to_json)