title: How can I make validate_media_type conditional?
body: <p>This is my Document model</p>
  
  <p>Document.rb</p>
  
  <pre><code>has_attached_file :document, validate_media_type: false
  </code></pre>
  
  <p>In order to accept documents like '.srt' file, I had to add <code>validate_media_type: false</code> to the attachment but I want to make this <code>validate_media_type</code> conditional.</p>
  
  <p>So, if it's a .srt file, then validate_media_type will be <code>false</code> and for all other files it will be <code>true</code></p>
  
  <p>How can I make <code>validate_media_type: false</code> conditional in my Document model?</p>