First try to implement ArraySerializer

test/fixtures/poro.rb

@@ -5,12 +5,16 @@ class Model
 
   def read_attribute_for_serialization(name)
     if name == :id || name == 'id'
-      object_id
+      id
     else
       @attributes[name]
     end
   end
 
+  def id
+    @attributes[:id] || @attributes['id'] || object_id
+  end
+
   def method_missing(meth, *args)
     if meth.to_s =~ /^(.*)=$/
       @attributes[$1.to_sym] = args[0]
@@ -28,3 +32,18 @@ end
 class ProfileSerializer < ActiveModel::Serializer
   attributes :name, :description
 end
+
+Post = Class.new(Model)
+Comment = Class.new(Model)
+
+PostSerializer = Class.new(ActiveModel::Serializer) do
+  attributes :title, :body, :id
+
+  has_many :comments
+end
+
+CommentSerializer = Class.new(ActiveModel::Serializer) do
+  attributes :id, :body
+
+  belongs_to :post
+end