FlattenJson adapter no longer inherits Json adapter

lib/active_model/serializer/adapter.rb

@@ -112,12 +112,14 @@ def cache_check(serializer)
         end
       end
 
+      private
+
       def meta
         serializer.meta if serializer.respond_to?(:meta)
       end
 
       def meta_key
-        serializer.meta_key || 'meta'
+        serializer.meta_key || 'meta'.freeze
       end
 
       def root

lib/active_model/serializer/adapter/flatten_json.rb

@@ -1,6 +1,44 @@
 class ActiveModel::Serializer::Adapter::FlattenJson < ActiveModel::Serializer::Adapter::Json
-        def serializable_hash(options = {})
-          super.each_value.first
+        def serializable_hash(options = nil)
+          options ||= {}
+          if serializer.respond_to?(:each)
+            result = serializer.map { |s| FlattenJson.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

lib/active_model/serializer/adapter/json.rb

@@ -4,44 +4,12 @@ class ActiveModel::Serializer::Adapter::Json < ActiveModel::Serializer::Adapter
 
         def serializable_hash(options = nil)
           options ||= {}
-          if serializer.respond_to?(:each)
-            result = serializer.map { |s| FlattenJson.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
-
-          { root => result }
+          { root => FlattenJson.new(serializer).serializable_hash(options) }
         end
 
+        private
+
         def fragment_cache(cached_hash, non_cached_hash)
-          ActiveModel::Serializer::Adapter::Json::FragmentCache.new().fragment_cache(cached_hash, non_cached_hash)
+          ActiveModel::Serializer::Adapter::Json::FragmentCache.new.fragment_cache(cached_hash, non_cached_hash)
         end
 end