Bugfix: include nested has_many association

Currently, doing `include: author.bio` would work correctly, but not for
has_many associations such as `include: author.roles`. This fixes it.

The problem was basically that we were not handling arrays for has_many linked,
as happens for ArraySerializers.

lib/active_model/serializer/adapter/json_api.rb

@@ -77,10 +77,13 @@ def add_linked(resource, serializer, parent = nil)
           resource_path = [parent, resource].compact.join('.')
           if include_assoc? resource_path
             plural_name = resource.to_s.pluralize.to_sym
-            attrs = attributes_for_serializer(serializer, @options)
+            attrs = [attributes_for_serializer(serializer, @options)].flatten
             @top[:linked] ||= {}
             @top[:linked][plural_name] ||= []
-            @top[:linked][plural_name].push attrs unless @top[:linked][plural_name].include? attrs
+
+            attrs.each do |attrs|
+              @top[:linked][plural_name].push(attrs) unless @top[:linked][plural_name].include?(attrs)
+            end
           end
 
           serializer.each_association do |name, association, opts|
@@ -91,9 +94,19 @@ def add_linked(resource, serializer, parent = nil)
         private
 
         def attributes_for_serializer(serializer, options)
-          attributes = serializer.attributes(options)
-          attributes[:id] = attributes[:id].to_s if attributes[:id]
-          attributes
+          if serializer.respond_to?(:each)
+            result = []
+            serializer.each do |object|
+              attributes = object.attributes(options)
+              attributes[:id] = attributes[:id].to_s if attributes[:id]
+              result << attributes
+            end
+          else
+            result = serializer.attributes(options)
+            result[:id] = result[:id].to_s if result[:id]
+          end
+
+          result
         end
 
         def include_assoc?(assoc)

test/action_controller/json_api_linked_test.rb

@@ -5,12 +5,15 @@ module Serialization
     class JsonApiLinkedTest < ActionController::TestCase
       class MyController < ActionController::Base
         def setup_post
+          @role1 = Role.new(id: 1, name: 'admin')
           @author = Author.new(id: 1, name: 'Steve K.')
           @author.posts = []
           @author.bio = nil
+          @author.roles = [@role1]
           @author2 = Author.new(id: 2, name: 'Anonymous')
           @author2.posts = []
           @author2.bio = nil
+          @author2.roles = []
           @post = Post.new(id: 1, title: 'New Post', body: 'Body')
           @first_comment = Comment.new(id: 1, body: 'ZOMG A COMMENT')
           @second_comment = Comment.new(id: 2, body: 'ZOMG ANOTHER COMMENT')
@@ -51,6 +54,13 @@ def render_resource_with_nested_include
           end
         end
 
+        def render_resource_with_nested_has_many_include
+          with_json_api_adapter do
+            setup_post
+            render json: @post, include: 'author,author.roles'
+          end
+        end
+
         def render_collection_without_include
           with_json_api_adapter do
             setup_post
@@ -82,6 +92,22 @@ def test_render_resource_with_include
         assert_equal 'Steve K.', response['linked']['authors'].first['name']
       end
 
+      def test_render_resource_with_nested_has_many_include
+        get :render_resource_with_nested_has_many_include
+        response = JSON.parse(@response.body)
+        expected_linked = {
+          "authors" => [{
+            "id" => "1",
+            "name" => "Steve K."
+          }],
+          "roles"=>[{
+            "id" => "1",
+            "name" => "admin"
+          }]
+        }
+        assert_equal expected_linked, response['linked']
+      end
+
       def test_render_resource_with_nested_include
         get :render_resource_with_nested_include
         response = JSON.parse(@response.body)

test/adapter/json_api/has_many_embed_ids_test.rb

@@ -8,6 +8,7 @@ class HasManyEmbedIdsTest < Minitest::Test
           def setup
             @author = Author.new(name: 'Steve K.')
             @author.bio = nil
+            @author.roles = nil
             @first_post = Post.new(id: 1, title: 'Hello!!', body: 'Hello, world!!')
             @second_post = Post.new(id: 2, title: 'New Post', body: 'Body')
             @author.posts = [@first_post, @second_post]

test/adapter/json_api/linked_test.rb

@@ -16,6 +16,7 @@ def setup
             @second_post.author = @author
             @author.posts = [@first_post, @second_post]
             @author.bio = @bio
+            @author.roles = []
             @bio.author = @author
 
             @serializer = ArraySerializer.new([@first_post, @second_post])

test/fixtures/poro.rb

@@ -40,6 +40,7 @@ class ProfileSerializer < ActiveModel::Serializer
 Author = Class.new(Model)
 Bio = Class.new(Model)
 Blog = Class.new(Model)
+Role = Class.new(Model)
 
 PostSerializer = Class.new(ActiveModel::Serializer) do
   attributes :title, :body, :id
@@ -60,9 +61,16 @@ class ProfileSerializer < ActiveModel::Serializer
   attributes :id, :name
 
   has_many :posts, embed: :ids
+  has_many :roles, embed: :ids
   belongs_to :bio
 end
 
+RoleSerializer = Class.new(ActiveModel::Serializer) do
+  attributes :id, :name
+
+  belongs_to :author
+end
+
 BioSerializer = Class.new(ActiveModel::Serializer) do
   attributes :id, :content
 

test/serializers/associations_test.rb

@@ -27,6 +27,7 @@ def method_missing(meth, *args)
       def setup
         @author = Author.new(name: 'Steve K.')
         @author.bio = nil
+        @author.roles = []
         @post = Post.new({ title: 'New Post', body: 'Body' })
         @comment = Comment.new({ id: 1, body: 'ZOMG A COMMENT' })
         @post.comments = [@comment]
@@ -42,6 +43,7 @@ def setup
       def test_has_many
         assert_equal(
           { posts: { type: :has_many, options: { embed: :ids } },
+            roles: { type: :has_many, options: { embed: :ids } },
             bio: { type: :belongs_to, options: {} } },
           @author_serializer.class._associations
         )
@@ -52,6 +54,9 @@ def test_has_many
           elsif name == :bio
             assert_equal({}, options)
             assert_nil serializer
+          elsif name == :roles
+            assert_equal({embed: :ids}, options)
+            assert_kind_of(ActiveModel::Serializer.config.array_serializer, serializer)
           else
             flunk "Unknown association: #{name}"
           end