title: Call a function after saving a model
body: <p>I'm working on a Django application connected to a LDAP server. Here's the trick i'm trying to do.</p>
  
  <p>I have a model called <em>system</em> containing some information about computers. When i add a new <em>system</em>, the model generates a unique UUID, like and AutoField. <strong>The point is that this parameter is generated when saving</strong>, and only the first time.<br>
  After saved, i need a function to keep that UUID and create a new object on my LDAP.<br>
  Since i didn't know a lot about signals, i tried overriding the model save function in this way:</p>
  
  <pre><code>def save(self):
  
          # import needed modules
          import ldap
          import ldap.modlist as modlist
  
          [--OPERATIONS ON THE LDAP--]
  
          super(System, self).save()
  </code></pre>
  
  <p>In this way, if i modify an existing <em>system</em> all work as should, because its UUID has been generated already. But if i try adding a new <em>system</em> i find the error UUID is None, and i can't work with an empty variable on LDAP (also it would be useless, don't u think so?)</p>
  
  <p>It seems i need to call the function that work on LDAP <strong>after the <em>system</em> is saved</strong>, and so after an UUID has been generated. I tried to unserstand how to create a post_save function but i couldn't get it.<br>
  How can i do that?</p>
  
  <p>Thanks</p>