Support has_one to be compatible with 0.8.x

lib/active_model/serializer.rb

@@ -49,6 +49,16 @@ def self.belongs_to(*attrs)
       associate(:belongs_to, attrs)
     end
 
+    # Defines an association in the object should be rendered.
+    #
+    # The serializer object should implement the association name
+    # as a method which should return an object when invoked. If a method
+    # with the association name does not exist, the association name is
+    # dispatched to the serialized object.
+    def self.has_one(*attrs)
+      associate(:has_one, attrs)
+    end
+
     def self.associate(type, attrs) #:nodoc:
       options = attrs.extract_options!
       self._associations = _associations.dup

test/adapter/json_api/has_one_test.rb

@@ -0,0 +1,43 @@
+require 'test_helper'
+
+module ActiveModel
+  class Serializer
+    class Adapter
+      class JsonApi
+        class HasOneTest < Minitest::Test
+          def setup
+            @author = Author.new(id: 1, name: 'Steve K.')
+            @bio = Bio.new(id: 43, content: 'AMS Contributor')
+            @author.bio = @bio
+            @bio.author = @author
+            @post = Post.new(id: 42, title: 'New Post', body: 'Body')
+            @anonymous_post = Post.new(id: 43, title: 'Hello!!', body: 'Hello, world!!')
+            @comment = Comment.new(id: 1, body: 'ZOMG A COMMENT')
+            @post.comments = [@comment]
+            @anonymous_post.comments = []
+            @comment.post = @post
+            @comment.author = nil
+            @post.author = @author
+            @anonymous_post.author = nil
+            @blog = Blog.new(id: 1, name: "My Blog!!")
+            @blog.writer = @author
+            @blog.articles = [@post, @anonymous_post]
+            @author.posts = []
+
+            @serializer = AuthorSerializer.new(@author)
+            @adapter = ActiveModel::Serializer::Adapter::JsonApi.new(@serializer, include: 'bio,posts')
+          end
+
+          def test_includes_bio_id
+            assert_equal("43", @adapter.serializable_hash[:authors][:links][:bio])
+          end
+
+          def test_includes_linked_bio
+            @adapter = ActiveModel::Serializer::Adapter::JsonApi.new(@serializer, include: 'bio')
+            assert_equal([{id: "43", :content=>"AMS Contributor"}], @adapter.serializable_hash[:linked][:bios])
+          end
+        end
+      end
+    end
+  end
+end

test/fixtures/poro.rb

@@ -60,7 +60,7 @@ class ProfileSerializer < ActiveModel::Serializer
   attributes :id, :name
 
   has_many :posts, embed: :ids
-  belongs_to :bio
+  has_one :bio
 end
 
 BioSerializer = Class.new(ActiveModel::Serializer) do

test/serializers/associations_test.rb

@@ -42,7 +42,7 @@ def setup
       def test_has_many
         assert_equal(
           { posts: { type: :has_many, options: { embed: :ids } },
-            bio: { type: :belongs_to, options: {} } },
+            bio: { type: :has_one, options: {} } },
           @author_serializer.class._associations
         )
         @author_serializer.each_association do |name, serializer, options|