title: Strip all characters except digits in Rails
body: <p>My users are giving these inputs</p>
  
  <p><code>123 - 4567 - 5665</code></p>
  
  <p><code>123124-124325</code></p>
  
  <p>But I need to submit them in form only with digits. Also I can't expect users to do it for me by giving them alerts. That would be too inconvenient for them.</p>
  
  <p>So result for in DB should be this <code>12345675665</code></p>
  
  <p>I'm using ruby on rails 4.2.</p>
  
  <p>What filter should I use and where?</p>