title: How to initialize new entry with some data in admin?
body: <p>I have a model:</p>
  
  <pre><code>class MyModel(models.Model):
      name = [...]
      surname = [...]
      symbol = models.CharField(unique=True)
      [...]
  </code></pre>
  
  <p>And I want to automatic generate some data in symbol field when user click "new" in admin panel. For example:</p>
  
  <pre><code>def generate_symbol():
      last_symbol = MyModel.objects.all().order_by('symbol')[0]
      return "%d" % (last_symbol + 1)
  </code></pre>
  
  <p>How to do it?</p>