Add a :root option to associations, which enables you to define what the root level key will be for the associated objects.

README.markdown

@@ -163,6 +163,30 @@ Assuming that the comments also `has_many :tags`, you will get a JSON like this:
 			{ "id": 3, "name": "happy" }
 		]
 	}
+	
+You can also specify a different root for the embedded objects than the key used to reference them, such as like this:
+
+	class PostSerializer < ApplicationSerializer
+		embed :ids, :include => true
+
+		attributes :id, :title, :body
+		has_many :comments, :key => :comment_ids, :root => :comment_objects
+	end
+	
+This would generate JSON that would look like this:
+
+	{
+		"post": {
+			"id": 1,
+			"title": "New post",
+			"body": "A body!",
+			"comment_ids": [ 1 ]
+		},
+		"comment_objects": [
+			{ "id": 1, "body": "what a dumb post" }
+		]
+	}
+
 
 **NOTE**: The `embed :ids` mechanism is primary useful for clients that process data in bulk and load it into a local store. For these clients, the ability to easily see all of the data per type, rather than having to recursively scan the data looking for information, is extremely useful.
 

lib/active_model/serializer.rb

@@ -146,6 +146,10 @@ module ActiveModel
           option(:key) || @name
         end
 
+        def root
+          option(:root) || plural_key
+        end
+
         def name
           option(:name) || @name
         end
@@ -454,7 +458,7 @@ module ActiveModel
         node[association.key] = association.serialize_ids
 
         if association.embed_in_root?
-          merge_association hash, association.plural_key, association.serialize_many, unique_values
+          merge_association hash, association.root, association.serialize_many, unique_values
         end
       elsif association.embed_objects?
         node[association.key] = association.serialize

test/serializer_test.rb

@@ -702,7 +702,56 @@ class SerializerTest < ActiveModel::TestCase
     expected = serializer_class.new(post).as_json
     assert_equal expected, hash_object
   end
+  
+  def test_embed_ids_include_true_with_root
+    serializer_class = post_serializer
 
+    serializer_class.class_eval do
+      root :post
+      embed :ids, :include => true
+      has_many :comments, :key => :comment_ids, :root => :comments
+      has_one :author, :serializer => DefaultUserSerializer, :key => :author_id, :root => :author
+    end
+
+    post = Post.new(:title => "New Post", :body => "Body of new post", :email => "tenderlove@tenderlove.com")
+    comments = [Comment.new(:title => "Comment1", :id => 1), Comment.new(:title => "Comment2", :id => 2)]
+    post.comments = comments
+
+    serializer = serializer_class.new(post)
+
+    assert_equal({
+    :post => {
+      :title => "New Post",
+      :body => "Body of new post",
+      :comment_ids => [1, 2],
+      :author_id => nil
+    },
+    :comments => [
+      { :title => "Comment1" },
+      { :title => "Comment2" }
+    ],
+    :author => []
+    }, serializer.as_json)
+
+    post.author = User.new(:id => 1)
+
+    serializer = serializer_class.new(post)
+
+    assert_equal({
+    :post => {
+      :title => "New Post",
+      :body => "Body of new post",
+      :comment_ids => [1, 2],
+      :author_id => 1
+    },
+    :comments => [
+      { :title => "Comment1" },
+      { :title => "Comment2" }
+    ],
+    :author => [{ :first_name => "Jose", :last_name => "Valim" }]
+    }, serializer.as_json)
+  end
+  
   # the point of this test is to illustrate that deeply nested serializers
   # still side-load at the root.
   def test_embed_with_include_inserts_at_root