Caching Image Uploads Across Page Loads with Rails -

caching image uploads across page loads rails problem

let’s imagine have form create blogpost title, body, , thumbnail image, , validate attributes present. this:

   <% if @post.errors.any? %>     <div>       <h2><%= pluralize(@post.errors.count, "error") %> prohibited post being saved:</h2>        <ul>       <% @post.errors.full_messages.each |msg| %>         <li><%= msg %></li>       <% end %>       </ul>     </div>   <% end %>    <div>     <%= f.label :title %>     <%= f.text_field :title %>   </div>   <div>     <%= f.label :body %>     <%= f.text_area :body %>   </div>   <div>     <%= f.label :thumbnail %>     <%= f.file_field :thumbnail %>   </div>   <div>     <%= f.submit %>   </div> <% end %> 

consider following sequence of events: user fills in body field, selects thumbnail upload, , submits form. form renders again because title missing. user fills in missing title , re-submits form.

uh oh! validations fail because image missing!

the user has find image wanted upload again, irritating. avoid making user irritated.

the solution: image caching

carrierwave has great functionality caching uploaded file across form re-renders.

under file field, let’s add:

<%= f.hidden_field :thumbnail_cache %> 

be sure add thumbnail_cache attr_accessible in rails 3, or permitted params in rails 4.

let’s add preview user can see current attached image:

<%= image_tag(@post.thumbnail_url) if @post.thumbnail? %> 

now if user submits form missing title, thumbnail image selection sticks around. irritation avoided. great success.

it works fine...

but how add value <%= f.file_field :thumbnail %>

i have no file chosen

i have thumbnail_cache - file name