Timedelta between two fields
<p>I'm looking for objects where the timedelta between two fields is greater than a certain number of days.</p>

<p>Baiscally I have a date when a letter is sent, and a date when an approval is received. When no approval is received in let's say 30 days, then these objects should be included in the queryset.</p>

<p>I can do something like the below, where the delta is something static.
However I don't need <code>datetime.date.today()</code> as a start but need to compare against the other object. </p>

<pre><code>delta = datetime.date.today() - datetime.timedelta(30)
return qs.filter(letter_sent__isnull=False)\
    .filter(approval_from__isnull=True)\
    .filter(letter_sent__gte=delta)
</code></pre>

<p>Any pointer how to do this?</p>