Move association serialization to association

lib/active_model/serializer/association.rb

@@ -29,6 +29,22 @@ module ActiveModel
       def meta
         options[:meta]
       end
+
+      # @api private
+      def serializable_hash(adapter_options, adapter_instance)
+        return options[:virtual_value] if options[:virtual_value]
+        object = serializer && serializer.object
+        return unless object
+
+        serialization = serializer.serializable_hash(adapter_options, {}, adapter_instance)
+
+        if options[:polymorphic] && serialization
+          polymorphic_type = object.class.name.underscore
+          serialization = { type: polymorphic_type, polymorphic_type.to_sym => serialization }
+        end
+
+        serialization
+      end
     end
   end
 end

lib/active_model/serializer/concerns/caching.rb

@@ -245,7 +245,7 @@ module ActiveModel
         non_cached_fields = fields[:non_cached].dup
         non_cached_hash = attributes(non_cached_fields, true)
         include_directive = JSONAPI::IncludeDirective.new(non_cached_fields - non_cached_hash.keys)
-        non_cached_hash.merge! resource_relationships({}, { include_directive: include_directive }, adapter_instance)
+        non_cached_hash.merge! associations_hash({}, { include_directive: include_directive }, adapter_instance)
 
         cached_fields = fields[:cached].dup
         key = cache_key(adapter_instance)
@@ -254,7 +254,7 @@ module ActiveModel
             fetch(adapter_instance, serializer_class._cache_options, key) do
               hash = attributes(cached_fields, true)
               include_directive = JSONAPI::IncludeDirective.new(cached_fields - hash.keys)
-              hash.merge! resource_relationships({}, { include_directive: include_directive }, adapter_instance)
+              hash.merge! associations_hash({}, { include_directive: include_directive }, adapter_instance)
             end
           end
         # Merge both results