How do I query the length of a Django ArrayField? : <p>I have an ArrayField in a model, I'm trying to annotate the length of this field ( so far without any luck) </p>

<p><code>F('field_name__len')</code> won't work since join is not allowed inside <code>F()</code>.  Even 
<code>ModelName.objets.values('field_name__len')</code> is not working</p>

<p>Any idea?</p>

<p>I'm using <strong>django 1.11</strong></p>
