Remove implicit constant lookup in serializers in favor active_model_serializer API.

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

lib/active_model/serializer.rb

@@ -80,32 +80,47 @@ module ActiveModel
         def key
           options[:key] || name
         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)
-          object && serializer.new(object, scope, options).serializable_hash
+        def serialize(object, scope, context, options)
+          { key => object && find_serializable(object, scope, context, options).as_json(:root => false) }
         end
 
         def serialize_ids(object, scope)
-          object && object.read_attribute_for_serialization(:id)
+          { key => object && object.read_attribute_for_serialization(:id) }
         end
       end
     end
@@ -141,12 +156,6 @@ module ActiveModel
           unless method_defined?(attr)
             class_eval "def #{attr}() object.#{attr} end", __FILE__, __LINE__
           end
-
-          options[:serializer] ||= begin
-            serializer_class = (options[:key] || attr).to_s.classify
-            const_get("#{serializer_class}Serializer")
-          end
-
           klass.new(attr, options)
         end
       end
@@ -286,6 +295,8 @@ 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]
@@ -303,7 +314,7 @@ 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
@@ -316,7 +327,7 @@ 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

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