title: How to check if a order has a shipment in Magento?
body: <p>I need to check if an order has already some shipment set. The only data I can use is the increment id of the order. I'm getting an instance of a model order, but I don't see a way I can get a shipment instance.</p>
  
  <p>I'm using this code:</p>
  
  <pre><code>$order = Mage::getModel('sales/order')
      -&gt;loadByIncrementId($order_increment_id);
  </code></pre>
  
  <p>But how can I get a shipment instance? I know that I can call <code>Mage::getModel('sales/order_shipment')-&gt;loadByIncrementId($shipment_increment_id)</code> but how do I get the shipment increment id?</p>