title: django: how many queries
body: <p>a noob question here.</p>
  
  <p>After reading the docs, I found that saving a model with a foreign key reference requires saving a model instance of the object being referenced.</p>
  
  <pre><code>a = ModelA.objects.get(pk=1)
  b = ModelB(foreignk = a,.....)
  b.save()
  </code></pre>
  
  <p>In this case, how many queries are actually executed? If I have the pk of the referenced model, is this the correct method to go ahead?</p>