docs: def update(id):
      """Update a post if the current user is the author."""
      post = get_post(id)
  
      if request.method == "POST":
          title = request.form["title"]
          body = request.form["body"]
          error = None
  
          if not title:
              error = "Title is required."
  
          if error is not None:
              flash(error)
          else:
              post.title = title
              post.body = body
              db.session.commit()
              return redirect(url_for("blog.index"))
  
      return render_template("blog/update.html", post=post)