Adding MySQL GROUP_CONCAT to doctrine in a Symfony project

config.yml

# app/config.yml

# ...

doctrine:
    orm:
        entity_managers:
            default:
                dql:
                    string_functions:
                        GROUP_CONCAT: Tentacode\LolCatBundle\Doctrine\Mysql\GroupConcat

GroupConcat.php

<?php

// src/Tentacode/LolcatBundle/Doctrine/Mysql/GroupConcat.php

namespace Tentacode\LolcatBundle\Doctrine\Mysql;

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

class GroupConcat extends FunctionNode
{
    protected $isDistinct = false;
    protected $expression = null;

    public function getSql(SqlWalker $sqlWalker)
    {
        return sprintf('GROUP_CONCAT(%s%s)',
            $this->isDistinct ? 'DISTINCT ' : '',
            $this->expression->dispatch($sqlWalker)
        );
    }

    public function parse(Parser $parser)
    {
        $parser->match(Lexer::T_IDENTIFIER);
        $parser->match(Lexer::T_OPEN_PARENTHESIS);

        $lexer = $parser->getLexer();
        if ($lexer->isNextToken(Lexer::T_DISTINCT)) {
            $parser->match(Lexer::T_DISTINCT);
            $this->isDistinct = true;
        }

        $this->expression = $parser->SingleValuedPathExpression();
        $parser->match(Lexer::T_CLOSE_PARENTHESIS);
    }
}

you can make a PR to https://github.com/luxifer/doctrine-functions ;)