ZF2 + Doctrine Custom Function Mysql DateDiff

DateDiff.php

<?php

namespace Application\DoctrineFunction;

use Doctrine\ORM\Query\Lexer;
use Doctrine\ORM\Query\AST\Functions\FunctionNode;

class DateDiff extends FunctionNode {
    /*
     * holds the timestamp of the DATE_FORMAT DQL statement
     * @var mixed
     */

    protected $dateInit;

    /**
     * holds the '%format' parameter of the DATE_FORMAT DQL statement
     * @var string
     */
    protected $dateEnd;

    /**
     * getSql - allows ORM  to inject a DATE_FORMAT() statement into an SQL string being constructed
     * @param \Doctrine\ORM\Query\SqlWalker $sqlWalker
     * @return void 
     */
    public function getSql(\Doctrine\ORM\Query\SqlWalker $sqlWalker) {
        return 'DATEDIFF(' .
                $sqlWalker->walkArithmeticExpression($this->dateInit) .
                ',' .
                $sqlWalker->walkStringPrimary($this->dateEnd) .
                ')';
    }

    /**
     * parse - allows DQL to breakdown the DQL string into a processable structure
     * @param \Doctrine\ORM\Query\Parser $parser 
     */
    public function parse(\Doctrine\ORM\Query\Parser $parser) {

        $parser->match(Lexer::T_IDENTIFIER);
        $parser->match(Lexer::T_OPEN_PARENTHESIS);

        $this->dateInit = $parser->ArithmeticExpression();
        $parser->match(Lexer::T_COMMA);


        $this->dateEnd = $parser->StringPrimary();
        $parser->match(Lexer::T_CLOSE_PARENTHESIS);
    }

}

doctrine.local.php

<?php

return array(
    'doctrine' => array(
        'configuration' => array(
            'orm_default' => array(
                'datetime_functions' => array(
                    'DATEDIFF' => 'Application\DoctrineFunction\DateDiff',
                )
            )
        ),
);

MyController.php

<?php

namespace Application\Controller;

class MyController{
    public function indexAction(){
        $qb = $this
                ->getOM()
                ->getRepository('Application\Entity\MyEntity')
                ->createQueryBuilder('q')
        $qb->select(array('DATEDIFF(q.date1, q.date2) as diff'));
        $result = $qb->getQuery()->getResult();
    }
    
}