title: ActiveRecord exists? with associations
body: <p>I have the following ActiveRecord call:</p>
  
  <pre><code>@payment = account.business.payments.find(params[:id])
  </code></pre>
  
  <p>Which searches through associations for a <code>payment</code> with id of <code>params[:id]</code>. However, this throws a RecordNotFound exception.</p>
  
  <p>I'd like to call <code>exists?</code> instead to see if the record exists to avoid throwing an exception. Doing <code>Payment.exists?(account.business.payments.find(params[:id]))</code> does not work.</p>
  
  <p>I'd like to search only the <code>payments</code> that <code>belong_to</code> that <code>business</code>, and not all payments by doing <code>Payment.exists?(:id =&gt; params[:id])</code>. That is so I can know that it's that particular account's business's payment.</p>
  
  <p>How can I do that?</p>
  
  <p>Note:
  <code>account</code> has_one <code>business</code> and <code>business</code> has_many <code>payments</code>.</p>