How to select randomly with Doctrine ODM?

Try this solution:

public function getRandomDocument()
{
    $qb = $this->getDocumentManager()->createQueryBuilder('YourBundle:TargetDocument');
    $count =  $qb->getQuery()->count();
    $skip_count = random_int(0, $count);
    $qb->skip($skip_count);
    return $qb->getQuery()->getSingleResult();
}

<?php
// Create Query Builder.
$dm = $this->getDocumentManager()->createQueryBuilder('Document');
// Count documents.
$count = $dm->getQuery()->execute()->count();
// Get random number not exceeding $count variable.
$random = mt_rand(0, $count);
// Query for document with skip.
$random_document = $dm->skip($random)
                      ->getQuery()
                      ->getSingleResult();

I'd do it like this:

Get a random id from your entities count, generate a random number based on the count, this will be the position of the entity to pick, something like this:

$count = 'SELECT COUNT(ID) FROM [your table]';
$random_position = rand(0, $count);
//select entity based on the id generated of your entity
//get your entity manager $em
$query = $em->createQuery("SELECT e FROM Project\Entity e");
$query->setFirstResult($random_position)->setMaxResult(1);
$entity = $query->getResult();

This should give you an starting point.