diff --git a/README.markdown b/README.md
similarity index 67%
rename from README.markdown
rename to README.md
index 94292668..aeb19a39 100644
--- a/README.markdown
+++ b/README.md
@@ -39,7 +39,7 @@ $ rails g resource post title:string body:string
 
 This will generate a serializer in `app/serializers/post_serializer.rb` for
 your new model. You can also generate a serializer for an existing model with
-the `serializer generator`:
+the serializer generator:
 
 ```
 $ rails g serializer post
@@ -66,10 +66,108 @@ end
 In this case, Rails will look for a serializer named `PostSerializer`, and if
 it exists, use it to serialize the `Post`. 
 
-This also works with `render_with`, which uses `to_json` under the hood. Also
+This also works with `respond_with`, which uses `to_json` under the hood. Also
 note that any options passed to `render :json` will be passed to your
 serializer and available as `@options` inside.
 
+To specify a custom serializer for an object, there are 2 options:
+
+#### 1. Specify the serializer in your model:
+
+```ruby
+class Post < ActiveRecord::Base
+  def active_model_serializer
+    FancyPostSerializer
+  end
+end
+```
+
+#### 2. Specify the serializer when you render the object:
+
+```ruby
+render :json => @post, :serializer => FancyPostSerializer
+```
+
+## Arrays
+
+In your controllers, when you use `render :json` for an array of objects, AMS will
+use `ActiveModel::ArraySerializer` (included in this project) as the base serializer,
+and the individual `Serializer` for the objects contained in that array.
+
+```ruby
+class PostSerializer < ActiveModel::Serializer
+  attributes :title, :body
+end
+
+class PostsController < ApplicationController
+  def index
+    @posts = Post.all
+    render :json => @posts
+  end
+end
+```
+
+Given the example above, the index action will return
+
+```json
+{
+  "posts":
+    [
+      { "title": "Post 1", "body": "Hello!" },
+      { "title": "Post 2", "body": "Goodbye!" }
+    ]
+}
+```
+
+By default, the root element is the name of the controller. For example, `PostsController`
+generates a root element "posts". To change it:
+
+```ruby
+render :json => @posts, :root => "some_posts"
+```
+
+You may disable the root element for arrays at the top level, which will result in
+more concise json. To disable the root element for arrays, you have 3 options:
+
+#### 1. Disable root globally for in `ArraySerializer`. In an initializer:
+
+```ruby
+ActiveModel::ArraySerializer.root = false
+```
+
+#### 2. Disable root per render call in your controller:
+
+```ruby
+render :json => @posts, :root => false
+```
+
+#### 3. Create a custom `ArraySerializer` and render arrays with it:
+
+```ruby
+class CustomArraySerializer < ActiveModel::ArraySerializer
+  self.root = false
+end
+
+# controller:
+render :json => @posts, :serializer => CustomArraySerializer
+```
+
+Disabling the root element of the array with any of the above 3 methods
+will produce
+
+```json
+[
+  { "title": "Post 1", "body": "Hello!" },
+  { "title": "Post 2", "body": "Goodbye!" }
+]
+```
+
+To specify a custom serializer for the items within an array:
+
+```ruby
+render :json => @posts, :each_serializer => FancyPostSerializer
+```
+
 ## Getting the old version
 
 If you find that your project is already relying on the old rails to_json
@@ -107,6 +205,45 @@ class PostSerializer < ActiveModel::Serializer
 end
 ```
 
+## Custom Attributes
+
+If you would like customize your JSON to include things beyond the simple 
+attributes of the model, you can override its `attributes` method 
+to return anything you need.
+
+The most common scenario to use this feature is when an attribute
+depends on a serialization scope. By default, the current user of your
+application will be available in your serializer under the method
+`scope`. This allows you to check for permissions before adding
+an attribute. For example:
+
+```ruby
+class Person < ActiveRecord::Base
+  def full_name
+    "#{first_name} #{last_name}"
+  end
+end
+
+class PersonSerializer < ActiveModel::Serializer
+  attributes :first_name, :last_name
+
+  def attributes
+    hash = super
+    hash["full_name"] = object.full_name if scope.admin?
+    hash
+  end
+end
+```
+
+The serialization scope can be customized in your controller by
+calling `serialization_scope`:
+
+```ruby
+class ApplicationController < ActionController::Base
+  serialization_scope :current_admin
+end
+```
+
 ## Associations
 
 For specified associations, the serializer will look up the association and
@@ -126,12 +263,12 @@ class PostSerializer < ActiveModel::Serializer
 
   # only let the user see comments he created.
   def comments
-    post.comments.where(:created_by => options[:scope])
+    post.comments.where(:created_by => scope)
   end
 end
 ```
 
-In a serializer, `options[:scope]` is the current authorization scope (usually
+In a serializer, `scope` is the current authorization scope (usually
 `current_user`), which the controller gives to the serializer when you call
 `render :json`
 
diff --git a/RELEASE_NOTES.md b/RELEASE_NOTES.md
index 00061b74..47bd7100 100644
--- a/RELEASE_NOTES.md
+++ b/RELEASE_NOTES.md
@@ -1,3 +1,14 @@
+# VERSION 0.6 (to be released)
+
+* Serialize sets properly
+* Add root option to ArraySerializer
+* Support polymorphic associations
+* Support :each_serializer in ArraySerializer
+* Add `scope` method to easily access the scope in the serializer
+* Fix regression with Rails 3.2.6
+* Allow serialization_scope to be disabled with serialization_scope nil
+* Array serializer should support pure ruby objects besides serializers
+
 # VERSION 0.5 (May 16, 2012)
 
 * First tagged version
diff --git a/lib/action_controller/serialization.rb b/lib/action_controller/serialization.rb
index 4230e1d0..b4cbc73d 100644
--- a/lib/action_controller/serialization.rb
+++ b/lib/action_controller/serialization.rb
@@ -40,15 +40,19 @@ module ActionController
     end
 
     def _render_option_json(json, options)
-      if json.respond_to?(:to_ary)
-        options[:root] ||= controller_name unless options[:root] == false
-      end
-
       serializer = options.delete(:serializer) ||
         (json.respond_to?(:active_model_serializer) && json.active_model_serializer)
 
+      if json.respond_to?(:to_ary)
+        if options[:root] != false && serializer.root != false
+          # default root element for arrays is serializer's root or the controller name
+          # the serializer for an Array is ActiveModel::ArraySerializer
+          options[:root] ||= serializer.root || controller_name
+        end
+      end
+
       if serializer
-        options[:scope] = serialization_scope
+        options[:scope] = serialization_scope unless options.has_key?(:scope)
         options[:url_options] = url_options
         json = serializer.new(json, options.merge(default_serializer_options || {}))
       end
diff --git a/lib/active_model/serializer.rb b/lib/active_model/serializer.rb
index fa1cfd19..cd743e4c 100644
--- a/lib/active_model/serializer.rb
+++ b/lib/active_model/serializer.rb
@@ -29,18 +29,31 @@ module ActiveModel
 
   # Active Model Array Serializer
   #
-  # It serializes an array checking if each element that implements
+  # It serializes an Array, checking if each element that implements
   # the +active_model_serializer+ method.
+  #
+  # To disable serialization of root elements:
+  #
+  #     ActiveModel::ArraySerializer.root = false
+  #
   class ArraySerializer
     attr_reader :object, :options
 
+    class_attribute :root
+
     def initialize(object, options={})
       @object, @options = object, options
     end
 
     def serializable_array
       @object.map do |item|
-        if item.respond_to?(:active_model_serializer) && (serializer = item.active_model_serializer)
+        if @options.has_key? :each_serializer
+          serializer = @options[:each_serializer]
+        elsif item.respond_to?(:active_model_serializer)
+          serializer = item.active_model_serializer
+        end
+
+        if serializer
           serializer.new(item, @options)
         else
           item
@@ -72,7 +85,7 @@ module ActiveModel
   #
   # Provides a basic serializer implementation that allows you to easily
   # control how a given object is going to be serialized. On initialization,
-  # it expects to object as arguments, a resource and options. For example,
+  # it expects two objects as arguments, a resource and options. For example,
   # one may do in a controller:
   #
   #     PostSerializer.new(@post, :scope => current_user).to_json
@@ -81,7 +94,7 @@ module ActiveModel
   # in for authorization purposes.
   #
   # We use the scope to check if a given attribute should be serialized or not.
-  # For example, some attributes maybe only be returned if +current_user+ is the
+  # For example, some attributes may only be returned if +current_user+ is the
   # author of the post:
   #
   #     class PostSerializer < ActiveModel::Serializer
@@ -97,11 +110,23 @@ module ActiveModel
   #       end
   #
   #       def author?
-  #         post.author == options[:scope]
+  #         post.author == scope
   #       end
   #     end
   #
   class Serializer
+    class IncludeError < StandardError
+      attr_reader :source, :association
+
+      def initialize(source, association)
+        @source, @association = source, association
+      end
+
+      def to_s
+        "Cannot serialize #{association} when #{source} does not have a root!"
+      end
+    end
+
     module Associations #:nodoc:
       class Config #:nodoc:
         class_attribute :options
@@ -176,6 +201,10 @@ module ActiveModel
           option(:include, source_serializer._root_embed)
         end
 
+        def embeddable?
+          !associated_object.nil?
+        end
+
       protected
 
         def find_serializable(object)
@@ -210,13 +239,41 @@ module ActiveModel
       end
 
       class HasOne < Config #:nodoc:
+        def embeddable?
+          if polymorphic? && associated_object.nil?
+            false
+          else
+            true
+          end
+        end
+
+        def polymorphic?
+          option :polymorphic
+        end
+
+        def polymorphic_key
+          associated_object.class.to_s.demodulize.underscore.to_sym
+        end
+
         def plural_key
-          key.to_s.pluralize.to_sym
+          if polymorphic?
+            associated_object.class.to_s.pluralize.demodulize.underscore.to_sym
+          else
+            key.to_s.pluralize.to_sym
+          end
         end
 
         def serialize
           object = associated_object
-          object && find_serializable(object).serializable_hash
+
+          if object && polymorphic?
+            { 
+              :type => polymorphic_key,
+              polymorphic_key => find_serializable(object).serializable_hash
+            }
+          elsif object
+            find_serializable(object).serializable_hash
+          end
         end
 
         def serialize_many
@@ -226,7 +283,14 @@ module ActiveModel
         end
 
         def serialize_ids
-          if object = associated_object
+          object = associated_object
+
+          if object && polymorphic?
+            { 
+              :type => polymorphic_key,
+              :id => object.read_attribute_for_serialization(:id)
+            }
+          elsif object
             object.read_attribute_for_serialization(:id)
           else
             nil
@@ -257,10 +321,12 @@ module ActiveModel
       end
 
       def attribute(attr, options={})
-        self._attributes = _attributes.merge(attr => options[:key] || attr)
+        self._attributes = _attributes.merge(attr => options[:key] || attr.to_s.gsub(/\?$/, '').to_sym)
 
         unless method_defined?(attr)
-          class_eval "def #{attr}() object.read_attribute_for_serialization(:#{attr}) end", __FILE__, __LINE__
+          define_method attr do
+            object.read_attribute_for_serialization(attr.to_sym)
+          end
         end
       end
 
@@ -270,7 +336,9 @@ module ActiveModel
 
         attrs.each do |attr|
           unless method_defined?(attr)
-            class_eval "def #{attr}() object.#{attr} end", __FILE__, __LINE__
+            define_method attr do
+              object.send attr
+            end
           end
 
           self._associations[attr] = klass.refine(attr, options)
@@ -387,7 +455,7 @@ module ActiveModel
     end
 
     def url_options
-      @options[:url_options]
+      @options[:url_options] || {}
     end
 
     # Returns a json representation of the serializable
@@ -475,7 +543,9 @@ module ActiveModel
       if association.embed_ids?
         node[association.key] = association.serialize_ids
 
-        if association.embed_in_root?
+        if association.embed_in_root? && hash.nil?
+          raise IncludeError.new(self.class, association.name)
+        elsif association.embed_in_root? && association.embeddable?
           merge_association hash, association.root, association.serialize_many, unique_values
         end
       elsif association.embed_objects?
@@ -514,6 +584,11 @@ module ActiveModel
       hash
     end
 
+    # Returns options[:scope]
+    def scope
+      @options[:scope]
+    end
+
     alias :read_attribute_for_serialization :send
 
     # Use ActiveSupport::Notifications to send events to external systems.
@@ -523,10 +598,3 @@ module ActiveModel
     end
   end
 end
-
-class Array
-  # Array uses ActiveModel::ArraySerializer.
-  def active_model_serializer
-    ActiveModel::ArraySerializer
-  end
-end
diff --git a/lib/active_model_serializers.rb b/lib/active_model_serializers.rb
index 38f4044e..3d44bac6 100644
--- a/lib/active_model_serializers.rb
+++ b/lib/active_model_serializers.rb
@@ -3,6 +3,7 @@ require "active_support/core_ext/string/inflections"
 require "active_support/notifications"
 require "active_model"
 require "active_model/serializer"
+require "set"
 
 if defined?(Rails)
   module ActiveModel
@@ -57,6 +58,19 @@ ActiveSupport.on_load(:active_record) do
   include ActiveModel::SerializerSupport
 end
 
+module ActiveModel::ArraySerializerSupport
+  def active_model_serializer
+    ActiveModel::ArraySerializer
+  end
+end
+
+Array.send(:include, ActiveModel::ArraySerializerSupport)
+Set.send(:include, ActiveModel::ArraySerializerSupport)
+
+ActiveSupport.on_load(:active_record) do
+  ActiveRecord::Relation.send(:include, ActiveModel::ArraySerializerSupport)
+end
+
 begin
   require 'action_controller'
   require 'action_controller/serialization'
diff --git a/test/serialization_test.rb b/test/serialization_test.rb
index d382f2ce..2bcc1c9a 100644
--- a/test/serialization_test.rb
+++ b/test/serialization_test.rb
@@ -66,6 +66,10 @@ class RenderJsonTest < ActionController::TestCase
     end
   end
 
+  class CustomArraySerializer < ActiveModel::ArraySerializer
+    self.root = "items"
+  end
+
   class TestController < ActionController::Base
     protect_from_forgery
 
@@ -127,13 +131,25 @@ class RenderJsonTest < ActionController::TestCase
       render :json => JsonSerializable.new, :options => true
     end
 
+    def render_json_with_serializer_and_scope_option
+      @current_user = Struct.new(:as_json).new(:current_user => true)
+      scope = Struct.new(:as_json).new(:current_user => false)
+      render :json => JsonSerializable.new, :scope => scope
+    end
+
     def render_json_with_serializer_api_but_without_serializer
       @current_user = Struct.new(:as_json).new(:current_user => true)
       render :json => JsonSerializable.new(true)
     end
 
+    # To specify a custom serializer for an object, use :serializer.
     def render_json_with_custom_serializer
-      render :json => [], :serializer => CustomSerializer
+      render :json => Object.new, :serializer => CustomSerializer
+    end
+
+    # To specify a custom serializer for each item in the Array, use :each_serializer.
+    def render_json_array_with_custom_serializer
+      render :json => [Object.new], :each_serializer => CustomSerializer
     end
 
     def render_json_with_links
@@ -144,6 +160,14 @@ class RenderJsonTest < ActionController::TestCase
       render :json => [], :root => false
     end
 
+    def render_json_empty_array
+      render :json => []
+    end
+
+    def render_json_array_with_custom_array_serializer
+      render :json => [], :serializer => CustomArraySerializer
+    end
+
 
   private
     def default_serializer_options
@@ -241,6 +265,11 @@ class RenderJsonTest < ActionController::TestCase
     assert_match '"options":true', @response.body
   end
 
+  def test_render_json_with_serializer_and_scope_option
+    get :render_json_with_serializer_and_scope_option
+    assert_match '"scope":{"current_user":false}', @response.body
+  end
+
   def test_render_json_with_serializer_api_but_without_serializer
     get :render_json_with_serializer_api_but_without_serializer
     assert_match '{"serializable_object":true}', @response.body
@@ -251,6 +280,11 @@ class RenderJsonTest < ActionController::TestCase
     assert_match '{"hello":true}', @response.body
   end
 
+  def test_render_json_array_with_custom_serializer
+    get :render_json_array_with_custom_serializer
+    assert_match '{"test":[{"hello":true}]}', @response.body
+  end
+
   def test_render_json_with_links
     get :render_json_with_links
     assert_match '{"link":"http://www.nextangle.com/hypermedia"}', @response.body
@@ -260,4 +294,23 @@ class RenderJsonTest < ActionController::TestCase
     get :render_json_array_with_no_root
     assert_equal '[]', @response.body
   end
+
+  def test_render_json_empty_array
+    get :render_json_empty_array
+    assert_equal '{"test":[]}', @response.body
+  end
+
+  def test_render_json_empty_arry_with_array_serializer_root_false
+    ActiveModel::ArraySerializer.root = false
+    get :render_json_empty_array
+    assert_equal '[]', @response.body
+  ensure # teardown
+    ActiveModel::ArraySerializer.root = nil
+  end
+
+  def test_render_json_array_with_custom_array_serializer
+    get :render_json_array_with_custom_array_serializer
+    assert_equal '{"items":[]}', @response.body
+  end
+
 end
diff --git a/test/serializer_support_test.rb b/test/serializer_support_test.rb
index b2d2b8be..2e963027 100644
--- a/test/serializer_support_test.rb
+++ b/test/serializer_support_test.rb
@@ -4,8 +4,27 @@ class RandomModel
   include ActiveModel::SerializerSupport
 end
 
+class RandomModelCollection
+  include ActiveModel::ArraySerializerSupport
+end
+
+module ActiveRecord
+  class Relation
+  end
+end
+
 class SerializerSupportTest < ActiveModel::TestCase
   test "it returns nil if no serializer exists" do
     assert_equal nil, RandomModel.new.active_model_serializer
   end
-end
\ No newline at end of file
+
+  test "it returns ArraySerializer for a collection" do
+    assert_equal ActiveModel::ArraySerializer, RandomModelCollection.new.active_model_serializer
+  end
+
+  test "it automatically includes array_serializer in active_record/relation" do
+    ActiveSupport.run_load_hooks(:active_record)
+    assert_equal ActiveModel::ArraySerializer, ActiveRecord::Relation.new.active_model_serializer
+  end
+end
+
diff --git a/test/serializer_test.rb b/test/serializer_test.rb
index 082cd6bf..8358178d 100644
--- a/test/serializer_test.rb
+++ b/test/serializer_test.rb
@@ -94,6 +94,11 @@ class SerializerTest < ActiveModel::TestCase
     has_many :comments, :serializer => CommentSerializer
   end
 
+  def test_scope_works_correct
+    serializer = ActiveModel::Serializer.new :foo, :scope => :bar
+    assert_equal serializer.scope, :bar
+  end
+
   def test_attributes
     user = User.new
     user_serializer = DefaultUserSerializer.new(user, {})
@@ -138,6 +143,12 @@ class SerializerTest < ActiveModel::TestCase
     assert_equal({ :host => "test.local" }, user_serializer.url_options)
   end
 
+  def test_serializer_returns_empty_hash_without_url_options
+    user = User.new
+    user_serializer = UserSerializer.new(user)
+    assert_equal({}, user_serializer.url_options)
+  end
+
   def test_pretty_accessors
     user = User.new
     user.superuser = true
@@ -411,6 +422,40 @@ class SerializerTest < ActiveModel::TestCase
     assert_equal({ :items => [ hash.as_json ]}, serializer.as_json)
   end
 
+  class CustomPostSerializer < ActiveModel::Serializer
+    attributes :title
+  end
+
+  def test_array_serializer_with_specified_seriailizer
+    post1 = Post.new(:title => "Post1", :author => "Author1", :id => 1)
+    post2 = Post.new(:title => "Post2", :author => "Author2", :id => 2)
+
+    array = [ post1, post2 ]
+
+    serializer = array.active_model_serializer.new array, :each_serializer => CustomPostSerializer
+
+    assert_equal([
+      { :title => "Post1" },
+      { :title => "Post2" }
+    ], serializer.as_json)
+  end
+
+  def test_sets_can_be_serialized
+    post1 = Post.new(:title => "Post1", :author => "Author1", :id => 1)
+    post2 = Post.new(:title => "Post2", :author => "Author2", :id => 2)
+
+    set = Set.new
+    set << post1
+    set << post2
+
+    serializer = set.active_model_serializer.new set, :each_serializer => CustomPostSerializer
+
+    as_json = serializer.as_json
+    assert_equal 2, as_json.size
+    assert as_json.include?({ :title => "Post1" })
+    assert as_json.include?({ :title => "Post2" })
+  end
+
   class CustomBlog < Blog
     attr_accessor :public_posts, :public_user
   end
@@ -890,4 +935,358 @@ class SerializerTest < ActiveModel::TestCase
     end
     assert_equal ActiveModel::Serializer, loaded
   end
+
+  def tests_query_attributes_strip_question_mark
+    todo = Class.new do
+      def overdue?
+        true
+      end
+
+      def read_attribute_for_serialization(name)
+        send name
+      end
+    end
+
+    serializer = Class.new(ActiveModel::Serializer) do
+      attribute :overdue?
+    end
+
+    actual = serializer.new(todo.new).as_json
+
+    assert_equal({
+      :overdue => true
+    }, actual)
+  end
+
+  def tests_query_attributes_allow_key_option
+    todo = Class.new do
+      def overdue?
+        true
+      end
+
+      def read_attribute_for_serialization(name)
+        send name
+      end
+    end
+
+    serializer = Class.new(ActiveModel::Serializer) do
+      attribute :overdue?, :key => :foo
+    end
+
+    actual = serializer.new(todo.new).as_json
+
+    assert_equal({
+      :foo => true
+    }, actual)
+  end
+
+  # Set up some classes for polymorphic testing
+  class Attachment < Model
+    def attachable
+      @attributes[:attachable]
+    end
+
+    def readable
+      @attributes[:readable]
+    end
+
+    def edible
+      @attributes[:edible]
+    end
+  end
+
+  def tests_can_handle_polymorphism
+    email_serializer = Class.new(ActiveModel::Serializer) do
+      attributes :subject, :body
+    end
+
+    email_class = Class.new(Model) do
+      def self.to_s
+        "Email"
+      end
+
+      define_method :active_model_serializer do
+        email_serializer
+      end
+    end
+
+    attachment_serializer = Class.new(ActiveModel::Serializer) do
+      attributes :name, :url
+      has_one :attachable, :polymorphic => true
+    end
+
+    email = email_class.new :subject => 'foo', :body => 'bar'
+
+    attachment = Attachment.new :name => 'logo.png', :url => 'http://example.com/logo.png', :attachable => email
+
+    actual = attachment_serializer.new(attachment, {}).as_json
+
+    assert_equal({
+      :name => 'logo.png', 
+      :url => 'http://example.com/logo.png',
+      :attachable => {
+        :type => :email,
+        :email => { :subject => 'foo', :body => 'bar' }
+      }
+    }, actual)
+  end
+
+  def test_can_handle_polymoprhic_ids
+    email_serializer = Class.new(ActiveModel::Serializer) do
+      attributes :subject, :body
+    end
+
+    email_class = Class.new(Model) do
+      def self.to_s
+        "Email"
+      end
+
+      define_method :active_model_serializer do
+        email_serializer
+      end
+    end
+
+    attachment_serializer = Class.new(ActiveModel::Serializer) do
+      embed :ids
+      attributes :name, :url
+      has_one :attachable, :polymorphic => true
+    end
+
+    email = email_class.new :id => 1
+
+    attachment = Attachment.new :name => 'logo.png', :url => 'http://example.com/logo.png', :attachable => email
+
+    actual = attachment_serializer.new(attachment, {}).as_json
+
+    assert_equal({
+      :name => 'logo.png', 
+      :url => 'http://example.com/logo.png',
+      :attachable => {
+        :type => :email,
+        :id => 1
+      }
+    }, actual)
+  end
+
+  def test_polymorphic_associations_are_included_at_root
+    email_serializer = Class.new(ActiveModel::Serializer) do
+      attributes :subject, :body, :id
+    end
+
+    email_class = Class.new(Model) do
+      def self.to_s
+        "Email"
+      end
+
+      define_method :active_model_serializer do
+        email_serializer
+      end
+    end
+
+    attachment_serializer = Class.new(ActiveModel::Serializer) do
+      root :attachment
+      embed :ids, :include => true
+      attributes :name, :url
+      has_one :attachable, :polymorphic => true
+    end
+
+    email = email_class.new :id => 1, :subject => "Hello", :body => "World"
+
+    attachment = Attachment.new :name => 'logo.png', :url => 'http://example.com/logo.png', :attachable => email
+
+    actual = attachment_serializer.new(attachment, {}).as_json
+
+    assert_equal({
+      :attachment => {
+        :name => 'logo.png', 
+        :url => 'http://example.com/logo.png',
+        :attachable => {
+          :type => :email, 
+          :id => 1
+        }},
+      :emails => [{
+        :id => 1,
+        :subject => "Hello",
+        :body => "World"
+      }]
+    }, actual)
+  end
+
+  def test_multiple_polymorphic_associations
+    email_serializer = Class.new(ActiveModel::Serializer) do
+      attributes :subject, :body, :id
+    end
+
+    orange_serializer = Class.new(ActiveModel::Serializer) do
+      embed :ids, :include => true
+
+      attributes :plu, :id
+      has_one :readable, :polymorphic => true
+    end
+
+    email_class = Class.new(Model) do
+      def self.to_s
+        "Email"
+      end
+
+      define_method :active_model_serializer do
+        email_serializer
+      end
+    end
+
+    orange_class = Class.new(Model) do
+      def self.to_s
+        "Orange"
+      end
+
+      def readable
+        @attributes[:readable]
+      end
+
+      define_method :active_model_serializer do
+        orange_serializer
+      end
+    end
+
+    attachment_serializer = Class.new(ActiveModel::Serializer) do
+      root :attachment
+      embed :ids, :include => true
+
+      attributes :name, :url
+
+      has_one :attachable, :polymorphic => true
+      has_one :readable,   :polymorphic => true
+      has_one :edible,     :polymorphic => true
+    end
+
+    email  = email_class.new  :id => 1, :subject => "Hello", :body => "World"
+    orange = orange_class.new :id => 1, :plu => "3027",  :readable => email
+
+    attachment = Attachment.new({
+      :name       => 'logo.png',
+      :url        => 'http://example.com/logo.png',
+      :attachable => email,
+      :readable   => email,
+      :edible     => orange
+    })
+
+    actual = attachment_serializer.new(attachment, {}).as_json
+
+    assert_equal({
+      :emails => [{
+        :subject => "Hello",
+        :body => "World",
+        :id => 1
+      }],
+
+      :oranges => [{
+        :plu => "3027",
+        :id => 1,
+        :readable => { :type => :email, :id => 1 }
+      }],
+
+      :attachment => {
+        :name => 'logo.png',
+        :url => 'http://example.com/logo.png',
+        :attachable => { :type => :email, :id => 1 },
+        :readable => { :type => :email, :id => 1 },
+        :edible => { :type => :orange, :id => 1 }
+      }
+    }, actual)
+  end
+
+  def test_raises_an_error_when_a_child_serializer_includes_associations_when_the_source_doesnt
+    attachment_serializer = Class.new(ActiveModel::Serializer) do
+      attributes :name
+    end
+
+    fruit_serializer = Class.new(ActiveModel::Serializer) do
+      embed :ids, :include => true
+      has_one :attachment, :serializer => attachment_serializer
+      attribute :color
+    end
+
+    banana_class = Class.new Model do
+      def self.to_s
+        'banana'
+      end
+
+      def attachment
+        @attributes[:attachment]
+      end
+
+      define_method :active_model_serializer do
+        fruit_serializer
+      end
+    end
+
+    strawberry_class = Class.new Model do
+      def self.to_s
+        'strawberry'
+      end
+
+      def attachment
+        @attributes[:attachment]
+      end
+
+      define_method :active_model_serializer do
+        fruit_serializer
+      end
+    end
+
+    smoothie = Class.new do
+      attr_reader :base, :flavor
+
+      def initialize(base, flavor)
+        @base, @flavor = base, flavor
+      end
+    end
+
+    smoothie_serializer = Class.new(ActiveModel::Serializer) do
+      root false
+      embed :ids, :include => true
+
+      has_one :base, :polymorphic => true
+      has_one :flavor, :polymorphic => true
+    end
+
+    banana_attachment = Attachment.new({
+      :name => 'banana_blending.md',
+      :id => 3,
+    })
+
+    strawberry_attachment = Attachment.new({
+      :name => 'strawberry_cleaning.doc',
+      :id => 4
+    })
+
+    banana = banana_class.new :color => "yellow", :id => 1, :attachment => banana_attachment
+    strawberry = strawberry_class.new :color => "red", :id => 2, :attachment => strawberry_attachment
+
+    smoothie = smoothie_serializer.new(smoothie.new(banana, strawberry))
+
+    assert_raise ActiveModel::Serializer::IncludeError do
+      smoothie.as_json
+    end
+  end
+
+  def tests_includes_does_not_include_nil_polymoprhic_associations
+    post_serializer = Class.new(ActiveModel::Serializer) do
+      root :post
+      embed :ids, :include => true
+      has_one :author, :polymorphic => true
+      attributes :title
+    end
+
+    post = Post.new(:title => 'Foo')
+
+    actual = post_serializer.new(post).as_json
+
+    assert_equal({
+      :post => {
+        :title => 'Foo',
+        :author => nil
+      }
+    }, actual)
+  end
 end