Improve polymorphic associations

README.textile

@@ -456,36 +456,7 @@ The +association_ids+ helper will use the overridden version of the association,
 this case, +association_ids+ will only include the ids of the comments provided by the
 +comments+ method.
 
-
-h3. Special Association Serializers
-
-So far, associations defined in serializers use either the +as_json+ method on the model
-or the defined serializer for the association type. Sometimes, you may want to serialize
-associated models differently when they are requested as part of another resource than
-when they are requested on their own.
-
-For instance, we might want to provide the full comment when it is requested directly,
-but only its title when requested as part of the post. To achieve this, you can define
-a serializer for associated objects nested inside the main serializer.
-
-<pre lang="ruby">
-class PostSerializer < ActiveModel::Serializer
-  class CommentSerializer < ActiveModel::Serializer
-    attributes :id, :title
-  end
-
-  # same as before
-  # ...
-end
-</pre>
-
-In other words, if a +PostSerializer+ is trying to serialize comments, it will first
-look for +PostSerializer::CommentSerializer+ before falling back to +CommentSerializer+
-and finally +comment.as_json+.
-
-h3. Overriding the Defaults
-
-h4. Authorization Scope
+h3. Authorization Scope
 
 By default, the authorization scope for serializers is +:current_user+. This means
 that when you call +render json: @post+, the controller will automatically call

active_model_serializers.gemspec

@@ -11,9 +11,8 @@ Gem::Specification.new do |gem|
   gem.test_files    = `git ls-files -- {test,spec,features}/*`.split("\n")
   gem.name          = "active_model_serializers"
   gem.require_paths = ["lib"]
-  gem.version       = "0.0.1"
+  gem.version       = "0.1.0"
 
   gem.add_dependency 'activemodel', '~> 3.0'
-
   gem.add_development_dependency "rails", "~> 3.0"
 end

lib/active_model/serializer.rb

@@ -1,7 +1,5 @@
 require "active_support/core_ext/class/attribute"
-require "active_support/core_ext/string/inflections"
 require "active_support/core_ext/module/anonymous"
-require "set"
 
 module ActiveModel
   # Active Model Array Serializer
@@ -84,51 +82,64 @@ module ActiveModel
         def polymorphic?
           options[:polymorphic]
         end
+
+        protected
+
+        def find_serializable(object, scope, context, options)
+          if serializer
+            serializer.new(object, scope, options)
+          elsif object.respond_to?(:active_model_serializer) && (ams = object.active_model_serializer)
+            ams.new(object, scope, options)
+          else
+            object
+          end
+        end
       end
 
       class HasMany < Config #:nodoc:
-        def serialize(collection, scope, options)
-          collection.map do |item|
-            serializer.new(item, scope, options).serializable_hash
+        def serialize(collection, scope, context, options)
+          array = collection.map do |item|
+            find_serializable(item, scope, context, options).as_json(:root => false)
           end
+          { key => array }
         end
 
         def serialize_ids(collection, scope)
-          # use named scopes if they are present
+          # Use pluck or select_columns if available
           # return collection.ids if collection.respond_to?(:ids)
 
-          collection.map do |item|
+          array = collection.map do |item|
             item.read_attribute_for_serialization(:id)
           end
+
+          { key => array }
         end
       end
 
       class HasOne < Config #:nodoc:
-        def serialize(object, scope, options)
-          return unless object
-
+        def serialize(object, scope, context, options)
           if polymorphic?
-            polymorphic_type = object.class.to_s.demodulize
-            serializer_class = "#{object.class.to_s}Serializer".constantize
-
-            serializer_class.new(object, scope, options).serializable_hash.merge({
-              "#{name}_type".to_sym => polymorphic_type
-            })
+            if object
+              find_serializable(object, scope, context, options).as_json(:root => object.class.to_s.demodulize.underscore.to_sym)
+            else
+              {}
+            end
           else
-            serializer.new(object, scope, options).serializable_hash
+            { key => object && find_serializable(object, scope, context, options).as_json(:root => false) }
           end
         end
 
+
         def serialize_ids(object, scope)
-          return unless object
 
           if polymorphic?
             { 
-              :id => object.read_attribute_for_serialization(:id),
-              "#{name}_type".to_sym => object.class.to_s.demodulize
+              object.class.to_s.demodulize.underscore.to_sym => object.read_attribute_for_serialization(:id),
             }
+          elsif object
+            { key => object.read_attribute_for_serialization(:id) }
           else
-            object.read_attribute_for_serialization(:id)
+            { key => nil }
           end
         end
       end
@@ -165,12 +176,6 @@ module ActiveModel
           unless method_defined?(attr)
             class_eval "def #{attr}() object.#{attr} end", __FILE__, __LINE__
           end
-
-          options[:serializer] ||= options[:polymorphic] || begin
-            serializer_class = (options[:key] || attr).to_s.classify
-            const_get("#{serializer_class}Serializer")
-          end
-
           klass.new(attr, options)
         end
       end
@@ -225,6 +230,9 @@ module ActiveModel
       # methods, provided by default by ActiveRecord. You can implement these
       # methods on your custom models if you want the serializer's schema method
       # to work.
+      #
+      # TODO: This is currently coupled to Active Record. We need to
+      # figure out a way to decouple those two.
       def schema
         klass = model_class
         columns = klass.columns_hash
@@ -265,7 +273,6 @@ module ActiveModel
 
       def inherited(klass) #:nodoc:
         return if klass.anonymous?
-
         name = klass.name.demodulize.underscore.sub(/_serializer$/, '')
 
         klass.class_eval do
@@ -284,8 +291,9 @@ module ActiveModel
 
     # Returns a json representation of the serializable
     # object including the root.
-    def as_json(*)
-      if root = @options[:root] || _root
+    def as_json(options=nil)
+      options ||= {}
+      if root = options.fetch(:root, @options.fetch(:root, _root))
         @hash = hash = {}
         hash.merge!(root => serializable_hash)
         hash
@@ -307,6 +315,8 @@ module ActiveModel
       end
     end
 
+    # Merge associations for embed case by always adding
+    # root associations to the given hash.
     def merge_associations(hash, associations)
       associations.each do |key, value|
         if hash[key]
@@ -324,7 +334,7 @@ module ActiveModel
 
       _associations.each do |association|
         associated_object = send(association.name)
-        hash[association.key] = association.serialize(associated_object, scope, :hash => @hash)
+        hash.merge! association.serialize(associated_object, scope, self, :hash => @hash)
       end
 
       hash
@@ -337,7 +347,7 @@ module ActiveModel
 
       _associations.each do |association|
         associated_object = send(association.name)
-        hash[association.key] = association.serialize_ids(associated_object, scope)
+        hash.merge! association.serialize_ids(associated_object, scope)
       end
 
       hash

lib/active_model_serializers.rb

@@ -1,3 +1,5 @@
+require "active_support"
+require "active_support/core_ext/string/inflections"
 require "active_model"
 require "active_model/serializer"
 
@@ -5,14 +7,19 @@ module ActiveModel::SerializerSupport
   extend ActiveSupport::Concern
 
   module ClassMethods #:nodoc:
-    def active_model_serializer
-      return @active_model_serializer if defined?(@active_model_serializer)
+    if "".respond_to?(:safe_constantize)
+      def active_model_serializer
+        @active_model_serializer ||= "#{self.name}Serializer".safe_constantize
+      end
+    else
+      def active_model_serializer
+        return @active_model_serializer if defined?(@active_model_serializer)
 
-      # Use safe constantize when Rails 3.2 is out
-      begin
-        @active_model_serializer = "#{self.name}Serializer".constantize
-      rescue NameError => e
-        raise unless e.message =~ /uninitialized constant$/ && e.name.to_s == "#{self.name}Serializer"
+        begin
+          @active_model_serializer = "#{self.name}Serializer".constantize
+        rescue NameError => e
+          raise unless e.message =~ /uninitialized constant/
+        end
       end
     end
   end

test/serializer_support_test.rb

@@ -0,0 +1,11 @@
+require "test_helper"
+
+class RandomModel
+  include ActiveModel::SerializerSupport
+end
+
+class SerializerSupportTest < ActiveModel::TestCase
+  test "it returns nil if no serializer exists" do
+    assert_equal nil, RandomModel.new.active_model_serializer
+  end
+end

test/serializer_test.rb

@@ -78,8 +78,13 @@ class SerializerTest < ActiveModel::TestCase
       { :title => @comment.read_attribute_for_serialization(:title) }
     end
 
-    def as_json(*)
-      { :comment => serializable_hash }
+    def as_json(options=nil)
+      options ||= {}
+      if options[:root] == false
+        serializable_hash
+      else
+        { :comment => serializable_hash }
+      end
     end
   end
 
@@ -189,65 +194,17 @@ class SerializerTest < ActiveModel::TestCase
     }, json)
   end
 
-  def test_implicit_serializer
-    author_serializer = Class.new(ActiveModel::Serializer) do
-      attributes :first_name
-    end
-
-    blog_serializer = Class.new(ActiveModel::Serializer) do
-      const_set(:AuthorSerializer, author_serializer)
-      has_one :author
-    end
-
-    user = User.new
-    blog = Blog.new
-    blog.author = user
-
-    json = blog_serializer.new(blog, user).as_json
-    assert_equal({
-      :author => {
-        :first_name => "Jose"
-      }
-    }, json)
-  end
-
-  def test_implicit_serializer_for_has_many
-    blog_with_posts = Class.new(Blog) do
-      attr_accessor :posts
-    end
-
-    blog_serializer = Class.new(ActiveModel::Serializer) do
-      const_set(:PostSerializer, PostSerializer)
-      has_many :posts
-    end
-
-    user = User.new
-    blog = blog_with_posts.new
-    blog.posts = [Post.new(:title => 'test')]
-
-    json = blog_serializer.new(blog, user).as_json
-    assert_equal({
-     :posts => [{
-       :title => "test", 
-       :body => nil, 
-       :comments => []
-     }]
-    }, json)
-  end
-
   def test_overridden_associations
     author_serializer = Class.new(ActiveModel::Serializer) do
       attributes :first_name
     end
 
     blog_serializer = Class.new(ActiveModel::Serializer) do
-      const_set(:PersonSerializer, author_serializer)
-
       def person
         object.author
       end
 
-      has_one :person
+      has_one :person, :serializer => author_serializer
     end
 
     user = User.new
@@ -703,8 +660,7 @@ class SerializerTest < ActiveModel::TestCase
     serializer = polymorphic_serializer.new(blog, user)
 
     assert_equal({
-      :writer => {
-        :writer_type => 'PolymorphicUser',
+      :polymorphic_user => {
         :first_name => "Jose",
         :last_name => "Valim"
       }
@@ -728,10 +684,7 @@ class SerializerTest < ActiveModel::TestCase
     serializer = polymorphic_serializer.new(blog, user)
 
     assert_equal({
-      :writer => {
-        :writer_type => 'PolymorphicUser',
-        :id => 1
-      }
+      :polymorphic_user => 1
     }, serializer.as_json)
   end
 
@@ -757,7 +710,19 @@ class SerializerTest < ActiveModel::TestCase
     author = author_class.new(:id => 5, :name => "Tom Dale")
     post.author = author
 
-    hash = serializer_class.new(post, nil, :root => :blog_post)
+    assert_equal({
+      :blog_post => {
+        :title => "New Post",
+        :body => "It's a new post!",
+        :author => { :id => 5, :name => "Tom Dale" }
+      }
+    }, serializer_class.new(post, nil, :root => :blog_post).as_json)
+
+    assert_equal({
+      :title => "New Post",
+      :body => "It's a new post!",
+      :author => { :id => 5, :name => "Tom Dale" }
+    }, serializer_class.new(post, nil, :root => false).as_json)
 
     assert_equal({
       :blog_post => {
@@ -765,7 +730,13 @@ class SerializerTest < ActiveModel::TestCase
         :body => "It's a new post!",
         :author => { :id => 5, :name => "Tom Dale" }
       }
-    }, hash.as_json)
+    }, serializer_class.new(post, nil).as_json(:root => :blog_post))
+
+    assert_equal({
+      :title => "New Post",
+      :body => "It's a new post!",
+      :author => { :id => 5, :name => "Tom Dale" }
+    }, serializer_class.new(post, nil).as_json(:root => false))
   end
 
   def test_serializer_has_access_to_root_object