app/controllers/guests_controller.rb

@@ -5,21 +5,22 @@
 require 'csv'
 
 class GuestsController < ApplicationController
+  GUEST_PARAMS = { only: %i[id name status], include: { group: { only: %i[id name] } } }.freeze
   def index
     render json: Guest.includes(:group)
                       .left_joins(:group)
                       .order('groups.name' => :asc, name: :asc)
-                      .as_json(only: %i[id name status], include: { group: { only: %i[id name] } })
+                      .as_json(GUEST_PARAMS)
   end
 
   def create
-    Guest.create!(guest_params)
-    render json: {}, status: :created
+    guest = Guest.create!(guest_params)
+    render json: guest.as_json(GUEST_PARAMS), status: :created
   end
 
   def update
-    Guest.find(params[:id]).update!(guest_params)
-    render json: {}, status: :ok
+    guest = Guest.find(params[:id]).update!(guest_params)
+    render json: guest.as_json(GUEST_PARAMS), status: :ok
   end
 
   def destroy

app/serializers/serializable_guest.rb

@@ -5,16 +5,12 @@
 class SerializableGuest < JSONAPI::Serializable::Resource
   type 'guest'
 
-  attributes :id, :group_id, :status
+  attributes :id, :status
 
   attribute :name do
     @object.name
   end
 
-  attribute :group_name do
-    @object.group.name
-  end
-
   attribute :status do
     @object.status.capitalize
   end