Adding entry type using setContentFromPost
Relationships are always added as arrays of IDs, even if you are only relating a single element:

$user-&gt;setContentFromPost(array(
    'companyName' =&gt; $admin-&gt;companyName, 
    'companyId' =&gt; $admin-&gt;companyId, 
    'partnerManager' =&gt; array($admin-&gt;partnerManager[0]-&gt;id)
));