Challenge 3: render vs redirect_to — Solution

class ProductsController < ApplicationController
  def update
    @product = Product.find(params[:id])
    if @product.update(product_params)
      redirect_to @product
    else
      render :edit
      # If redirect_to :edit were used here instead of render :edit, the
      # browser would make a brand new GET request to the edit page --
      # which would reload @product fresh from the database (discarding
      # the invalid changes the user just tried to submit) and lose the
      # validation error messages entirely, since those only exist on the
      # @product instance built during THIS failed update attempt. The
      # user would see a blank, unhelpful edit form with no indication of
      # what went wrong, instead of their original input plus error text.
    end
  end
end

=begin
Notes:
- redirect_to @product on success sends a fresh GET request to the
  product's show page, correctly reflecting the just-saved changes with a
  clean URL in the browser's address bar.
- render :edit on failure re-renders the SAME @product object that just
  failed to save -- including both the user's submitted (invalid) values
  and any validation error messages attached to it -- without a new
  request being made at all.
- The core rule from the chapter: render for "same request, show
  something related to what just happened"; redirect_to for "this
  succeeded, send the user somewhere new."
=end