Selecting random DB entry in Symfony2 - Getting an error - php

Question

I have been trying to pull out a random row, I have used this:
This is the example code I found which did not really help ( I found here: https://gist.github.com/pierroweb/1518601)
class QuestionRepository extends EntityRepository
{
public function findOneRandom()
{
$em = $this->getEntityManager();
$max = $em->createQuery('
SELECT MAX(q.id) FROM EnzimQuestionBundle:Question q
')
->getSingleScalarResult();
return $em->createQuery('
SELECT q FROM EnzimQuestionBundle:Question q
WHERE q.id >= :rand
ORDER BY q.id ASC
')
->setParameter('rand',rand(0,$max))
->setMaxResults(1)
->getSingleResult();
}
}
Now I have something like this:
$em = $this->getEntityManager();
$max = $em->createQuery('SELECT MAX(p.id) FROM GreenMonkeyDevGlassShopBundle:Product p')->getSingleScalarResult();
return $em->createQuery('SELECT p FROM GreenMonkeyDevGlassShopBundle:Product p INNER JOIN (SELECT p2.categories. FROM GreenMonkeyDevGlassShopBundle:Product p.categories WHERE :cid IN(pc) p.id >= :rand ORDER BY p.id ASC')
->setParameter('cid', $category_id)
->setParameter('rand',rand(0,$max))
->setMaxResults(intval($limit))
->getSingleResult();
I keep getting this error though:
FatalErrorException: Error: Call to undefined method Doctrine\ORM\Query\ResultSetMapping::addRootEntityFromClassMetadata() in /var/www/gmd-milkywayglass/src/GreenMonkeyDev/GlassShopBundle/Entity/CategoryRepository.php line 42
Any thoughts on what I can be doing wrong? I know that Doctrine does not have a get random method. Maybe there is some simple solution? Thank you!

Answer 1

You should try to write your own DQL function in order to use RAND() in your query :
namespace My\Custom\Doctrine2\Function;
/**
* RandFunction ::= "RAND" "(" ")"
*/
class Rand extends FunctionNode
{
public function parse(\Doctrine\ORM\Query\Parser $parser)
{
$parser->match(Lexer::T_IDENTIFIER);
$parser->match(Lexer::T_OPEN_PARENTHESIS);
$parser->match(Lexer::T_CLOSE_PARENTHESIS);
}
public function getSql(\Doctrine\ORM\Query\SqlWalker $sqlWalker)
{
return 'RAND()';
}
}
After you have to register this DQL function in symfony2 config.yml
doctrine:
dbal:
# ...
orm:
#...
dql:
numeric_functions:
RAND: My\Custom\Doctrine2\Function
For more informations, read the following links
DQL User Defined Functions
How to Register Custom DQL Functions in Symfony2