Answered HowTo: list resource documents of a resource container in a CMP?

public function prepareQueryBeforeCount(xPDOQuery $c) {
    $parent = $this->getProperty('parent');
    if (!empty($parent)) {
        $resourceColumns = array(
            'id'
            ,'pagetitle'
            ,'parent'
            ,'published'
        );

        $joinclass = 'modUser';
        $joinalias = 'PublishedBy';
        $c->leftjoin($joinclass, $joinalias);
        $c->select($this->modx->getSelectColumns($this->classKey, 'modResource', '', $resourceColumns));
        $c->select($this->modx->getSelectColumns($joinclass, $joinalias, 'publishedby_'));
        $c->where(array('modResource.parent:=' => $parent));
        $c->where(array('modResource.deleted' => 0));
    }
    return $c;
}

$c->select($this->modx->getSelectColumns($joinclass, $joinalias, 'publishedby_'));

$c->select($modx->getSelectColumns($joinclass, $joinalias, 'publishedby_'));