title: Getting the total of unit price * quantity
body: <p>Here's an excerpt from my models:</p>
  
  <pre><code>class Order(models.Model):
      ...
      content_type = models.ForeignKey(ContentType)
      user = models.ForeignKey('auth.User')
  
  
  class OrderItem(models.Model):
      ...
      unit_price = models.DecimalField(max_digits=7, decimal_places=2, blank=True)
      quantity = models.SmallIntegerField()
      order = models.ForeignKey(Order)
  </code></pre>
  
  <p>I have a dashboard where I want to display the total of sold items. I am struggling with how I can multiply the <code>unit_price</code> by the <code>quantity</code>.</p>