title: ActiveAdmin to filter float fields on ActiveRecord models
body: <p>I found <a href="http://activeadmin.info" rel="nofollow">ActiveAdmin</a> very useful for creating rather full-brown scaffold for our ActiveRecord models. However, our models have float (and some decimal) columns and ActiveAdmin fails to create filters for them.</p>
  
  <p>For example,</p>
  
  <pre><code>ActiveAdmin.register ForexRate do
    filter :rate, :as =&gt; :numeric
  end
  </code></pre>
  
  <p>gives me NoMethodError, saying</p>
  
  <pre><code>undefined method `rate_gt' for #&lt;MetaSearch::Searches::ForexRate:0x007fa4427bb018&gt;
  </code></pre>
  
  <p>What am I doing wrong here? Thanks in advance!</p>
  
  <p>P.S. I have confirmed the same filter worked for integer columns.</p>