title: Open the temporary file before it is saved in Rails model
body: <p>Once you've uploaded a file, is it possible to open that file before the model is saved?</p>
  
  <p>I'm using Paperclip to save files in the /public folder.</p>
  
  <pre><code>class Book &lt; ActiveRecord::Base
    before_save :open_it
    has_attached_file :upload
  
    def open_it
      a_file = open(upload.url) # this doesn't work before save ?
      # ... 
    end
  end
  </code></pre>