From 3bba334cf875cd3d9f53c4d1f9673558f71139d6 Mon Sep 17 00:00:00 2001
From: Guillermo Iguaran <guilleiguaran@gmail.com>
Date: Fri, 31 Oct 2014 14:30:59 -0500
Subject: [PATCH] JSON-API: Don't include linked section if associations are
 empty

---
 lib/active_model/serializer/adapter/json_api.rb |  8 +++-----
 test/adapter/json_api/has_many_test.rb          | 10 ++++++++++
 2 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/lib/active_model/serializer/adapter/json_api.rb b/lib/active_model/serializer/adapter/json_api.rb
index de0f3f83..596d54c0 100644
--- a/lib/active_model/serializer/adapter/json_api.rb
+++ b/lib/active_model/serializer/adapter/json_api.rb
@@ -18,9 +18,6 @@ module ActiveModel
 
             serializer.each_association do |name, association, opts|
               @hash[@root][:links] ||= {}
-              unless opts[:embed] == :ids
-                @hash[:linked] ||= {}
-              end
 
               if association.respond_to?(:each)
                 add_links(name, association, opts)
@@ -47,7 +44,8 @@ module ActiveModel
             @hash[@root][:links][name][:ids] += serializers.map{|serializer| serializer.id.to_s }
           end
 
-          unless options[:embed] == :ids
+          unless options[:embed] == :ids || serializers.count == 0
+            @hash[:linked] ||= {}
             @hash[:linked][name] ||= []
             @hash[:linked][name] += serializers.map { |item| attributes_for_serializer(item, options) }
           end
@@ -66,7 +64,7 @@ module ActiveModel
 
             unless options[:embed] == :ids
               plural_name = name.to_s.pluralize.to_sym
-
+              @hash[:linked] ||= {}
               @hash[:linked][plural_name] ||= []
               @hash[:linked][plural_name].push attributes_for_serializer(serializer, options)
             end
diff --git a/test/adapter/json_api/has_many_test.rb b/test/adapter/json_api/has_many_test.rb
index 2f74195f..6bcd43ca 100644
--- a/test/adapter/json_api/has_many_test.rb
+++ b/test/adapter/json_api/has_many_test.rb
@@ -8,12 +8,15 @@ module ActiveModel
           def setup
             @author = Author.new(id: 1, name: 'Steve K.')
             @post = Post.new(id: 1, title: 'New Post', body: 'Body')
+            @post_without_comments = Post.new(id: 2, title: 'Second Post', body: 'Second')
             @first_comment = Comment.new(id: 1, body: 'ZOMG A COMMENT')
             @second_comment = Comment.new(id: 2, body: 'ZOMG ANOTHER COMMENT')
             @post.comments = [@first_comment, @second_comment]
+            @post_without_comments.comments = []
             @first_comment.post = @post
             @second_comment.post = @post
             @post.author = @author
+            @post_without_comments.author = nil
             @blog = Blog.new(id: 1, name: "My Blog!!")
             @blog.writer = @author
             @blog.articles = [@post]
@@ -33,6 +36,13 @@ module ActiveModel
                          ], @adapter.serializable_hash[:linked][:comments])
           end
 
+          def test_no_include_linked_if_comments_is_empty
+            serializer = PostSerializer.new(@post_without_comments)
+            adapter = ActiveModel::Serializer::Adapter::JsonApi.new(serializer)
+
+            assert_nil adapter.serializable_hash[:linked]
+          end
+
           def test_include_type_for_association_when_is_different_than_name
             serializer = BlogSerializer.new(@blog)
             adapter = ActiveModel::Serializer::Adapter::JsonApi.new(serializer)