title: Does django's `save()` create or update?
body: <p>The documentation just says</p>
  
  <blockquote>
    <p>To save an object back to the database, call save()</p>
  </blockquote>
  
  <p>That does not make it clear. Exprimenting, I found that if I include an <code>id</code>, it updates existing entry, while, if I don't, it creates a new row. Does the documentation specify what happens?</p>