Custom doctrine type to store uuid's as binary(16) values in a MySQL database. Set the column type that you want to use as BINARY(16) in MySQL and your good to go.

Doctrine.php

\Doctrine\DBAL\Types\Type::addType('uuid', 'BuboBox\Doctrine2\DBAL\Types\UuidType');

UuidType.php

<?php

namespace BuboBox\Doctrine2\DBAL\Types;

use Doctrine\DBAL\Types\Type;
use Doctrine\DBAL\Platforms\AbstractPlatform;

/**
 * Type that maps a PHP array to a clob SQL type.
 *
 * @since 2.0
 */
class UuidType extends Type
{

    const BINARY = 'binary';

    public function getSqlDeclaration(array $fieldDeclaration, AbstractPlatform $platform)
    {
        return sprintf('BINARY(%d)', $fieldDeclaration['length']);
    }

    public function getName()
    {       
        return self::BINARY;
    }   

    public function convertToPhpValue($value, AbstractPlatform $platform)
    {
        if ($value !== null) {
            $value= unpack('H*', $value);
            $hash = array_shift($value);
            $uuid = substr($hash,  0,  8) . '-' . substr($hash,  8,  4) . '-' . substr($hash, 12,  4) . '-' . substr($hash, 16,  4) . '-' . substr($hash, 20, 12);
            return $uuid;
        }
    }

    public function convertToDatabaseValue($value, AbstractPlatform $platform)
    {
        if ($value !== null) {
            return pack('H*', str_replace('-', '',$value));
        }
    }

}

Man, you just saved me hours of headache :)

Thanks for sharing this! Perhaps you want to checkout my fork as I've slightly updated the code a bit. For the reasoning behind this you might wanna checkout the post I wrote about it.