title: How do I generate a field from other fields in rails model
body: <p>I have an address split up into <code>@profile.street_address</code> , <code>@profile.region</code>, <code>@profile.zip_code</code>. </p>
  
  <p>I want to create </p>
  
  <pre><code>@profile.address = "#{@profile.street_address} #{@profile.region} #{@profile.zip_code}"
  </code></pre>
  
  <p>What is the best way to do this every time my model is created or updated? </p>