Define set_id method

Author: Shuhei Kitagawa

lib/fast_jsonapi/object_serializer.rb

@@ -128,6 +128,10 @@ def set_type(type_name)
         self.record_type = run_key_transform(type_name)
       end
 
+      def set_id(id_name)
+        self.record_id = id_name
+      end
+
       def cache_options(cache_options)
         self.cached = cache_options[:enabled] || false
         self.cache_length = cache_options[:cache_length] || 5.minutes