#10, #15 完了

backend/app/controllers/posts_controller.rb

@@ -18,13 +18,13 @@ class PostsController < ApplicationController
     else
       @posts = Post.all
     end
-    render json: @posts
+    render json: @posts.as_json(include: { tags: { only: [:id, :name, :category] } })
   end
 
   # GET /posts/1
   def show
     @post = Post.includes(:tags).find(params[:id])
-    render json: @post.as_json(include: { tags: { only: [:id, :name] } })
+    render json: @post.as_json(include: { tags: { only: [:id, :name, :category] } })
   end
 
   # POST /posts