title: Validates greater than existing column in rails model
body: <p>I want to validate on update that <code>:budget_price</code> is always greater than previous value existing in this column.</p>
  
  <p>I make a check on client side by html5 but how I validate it in model.rb</p>
  
  <p>I write </p>
  
  <pre><code>validates :budget_price, :numericality =&gt; { :greater_than =&gt; :budget_price }, :on =&gt; :update
  </code></pre>
  
  <p>But it doesn't work properly</p>