Convert SQL Query (+JOIN) to Symfony Propel query
<p>I have a sql query that works well on mysql (query + join): </p>

<pre><code>select sum(pa.price) 
from user u , purchase pu , pack pa 
where (u.username = pu.username) and (pu.idpack = pa.idpack)
</code></pre>

<p>I want to use this query in my <strong>symfony project (PROPEL ORM)</strong></p>

<p>How can I write it, please...</p>