title: How can you do a conditional where clause using AREL
body: <p>How can you do a conditional where clause?  I have a rake task that runs a query.  Say I am building a query like so:</p>
  
  <pre><code>residentials = Residential.where(:is_active =&gt; true)
  </code></pre>
  
  <p>Now if I pass a certain parameter to the rake task, I want to add to the where clause.  I was thinking something like this:</p>
  
  <pre><code>residentials.where(:something_else =&gt; true) if param_was_passed
  </code></pre>
  
  <p>But that just replaces the existing where clause.  How can I add it to the existing where clauses?</p>