#7

backend/app/models/post.rb

@@ -4,4 +4,12 @@ class Post < ApplicationRecord
   has_many :post_tags, dependent: :destroy
   has_many :tags, through: :post_tags
   has_many :user_post_views, dependent: :destroy
+  has_one_attached :thumbnail
+
+  def as_json options = { }
+    super(options).merge({ thumbnail: thumbnail.attached? ?
+                                      Rails.application.routes.url_helpers.rails_blob_url(
+                                          thumbnail, only_path: false) :
+                                      nil })
+  end
 end