Rename FlattenJson to Attributes (allow plural adapter names)

lib/active_model/serializer/adapter/attributes.rb

@@ -0,0 +1,50 @@
+class ActiveModel::Serializer::Adapter::Attributes < ActiveModel::Serializer::Adapter
+        def serializable_hash(options = nil)
+          options ||= {}
+          if serializer.respond_to?(:each)
+            result = serializer.map { |s| Attributes.new(s).serializable_hash(options) }
+          else
+            hash = {}
+
+            core = cache_check(serializer) do
+              serializer.attributes(options)
+            end
+
+            serializer.associations.each do |association|
+              serializer = association.serializer
+              association_options = association.options
+
+              if serializer.respond_to?(:each)
+                array_serializer = serializer
+                hash[association.key] = array_serializer.map do |item|
+                  cache_check(item) do
+                    item.attributes(association_options)
+                  end
+                end
+              else
+                hash[association.key] =
+                  if serializer && serializer.object
+                    cache_check(serializer) do
+                      serializer.attributes(options)
+                    end
+                  elsif association_options[:virtual_value]
+                    association_options[:virtual_value]
+                  end
+              end
+            end
+            result = core.merge hash
+          end
+          result
+        end
+
+        def fragment_cache(cached_hash, non_cached_hash)
+          Json::FragmentCache.new.fragment_cache(cached_hash, non_cached_hash)
+        end
+
+        private
+
+        # no-op: Attributes adapter does not include meta data, because it does not support root.
+        def include_meta(json)
+          json
+        end
+end