title: Process attachment after upload with Paperclip
body: <p>I'am using gems:</p>
  
  <pre><code>gem 'rails', '4.2.1'
  gem 'mongoid','~&gt;4.0.2'
  gem "paperclip", "~&gt; 4.2"
  gem 'mongoid-paperclip'
  </code></pre>
  
  <p>I need process (parse some csv) when is file uploaded.</p>
  
  <p>My code:</p>
  
  <pre><code>class MyModel
    #... mongoid and paperclip configuration
    after_save :parse_csv
  
    def parse_csv
      puts self.spreadsheet.path #works - path is correct
      puts self.spreadsheet.url #works - url is correct
      File.open self.spreadsheet.path #No such file or directory
  end
  </code></pre>
  
  <p>How I can process files with after_save (or create) with Paperclip and Mongoid? In my callback, file still isn't saved on the file system.</p>