title: how to customize rails activerecord validation error message to show attribute value
body: <p>When a user tries to create a record with a name that already exists, I want to show an error message like:</p>
  
  <p><code>name "some name" has already been taken</code></p>
  
  <p>I have been trying to do:</p>
  
  <pre><code>validates_uniqueness_of :name, :message =&gt; "#{name} has already been taken"
  </code></pre>
  
  <p>but this outputs the table name instead of the value of the name attribute</p>