title: ActiveRecord#exists? or rescue from ActiveRecord::RecordNotFound
body: <p>What is the recommended way of handling the following type of situations:</p>
  
  <p>Supposing I have a model called <code>Cart</code>, that has a 1-1 relationship with the model <code>Person</code> and the same PK (the user's id).
  <br /><br />In the <code>index</code> method of my <code>cart_controller</code> I want to check if a <code>Cart</code> exists for the current user.
  If I do <code>Cart.find(the_user_id)</code> and a cart doesn't exists a <code>RecordNotFound</code> exception gets raised.
  <br />I see two ways of solving this:</p>
  
  <h3>1. rescue from the exception</h3>
  
  <pre><code> begin
      @cart = Cart.find(the_user_id)
      #more code here
   rescue ActiveRecord::RecordNotFound
      #the cart is empty message
   end
  </code></pre>
  
  <h3>2. use ActiveRecord#exists? method</h3>
  
  <pre><code> if Cart.exists?(the_user_id)
      @cart = Cart.find(the_user_id)
      #more code here
   else
      #the cart is empty message
   end
  </code></pre>
  
  <p>From my (limited) knowledge on exeption handling I know that it's not recommended to use exceptions this way, but is making an extra query every time worth it?</p>