Modx 2 get document by alias

$columns = array_keys($modx->getFields('modResource'));

$criteria = $modx->newQuery('modResource');

$criteria->setClassAlias('sc');

$criteria->select($columns);

$criteria->andCondition("sc.published=1 and sc.deleted=0 and sc.alias='" . mysql_escape_string($alias) . "'");

$criteria->limit(1);

//$criteria->prepare();

//return $criteria->toSQL();

$objCollection = $modx->getCollection('modResource', $criteria);

$collection = array();

foreach ($objCollection as $obj) {

array_push($collection, $obj->get($columns));

}

if (count($collection) <>

return $collection[0]["content"];