Active Storage: Best practice to retain/cache uploaded file when form redisplays

for those looking for has_many_attached solution

https://github.com/rails/rails/issues/35817#issuecomment-484158884

<% if @product.photos.attached? %>
  <% @product.photos.each do |ph| %>
    <%= f.hidden_field :photos, value: ph.signed_id %>
  <% end %>
<% end %>

Here's a solution to make ActiveStorage files persist on form redisplay: f.hidden_field :image, value: f.object.image.signed_id if f.object.image.attached? f.file_field :image