Doctrine2: using the querybuilder for many-to-many relationships - symfony

Question

To search people in a system I have written a function in a repository.
This function receives an array with field names and criteria, and uses the querybuilder to formulate a valid DQL-statement.
Everything works fine, until the moment I want to make a search rule like:
"Find all people that belong to a certain domain."
...where the Person and Domain entities have a many-to-many relationship.
According to Symfony2 that relationship is defined correctly, and indeed everything works in Twig templates and controllers.
The function looks as follows:-
private function query($extra_conditions = null)
{
$qb = $this->_em->createQueryBuilder();
$query =
$qb->select('p')
->from('AppMainBundle:Person', 'p')
->leftjoin('AppMainBundle:Domain', 'd')
->where("p.firstname IS NOT NULL")
->andWhere("p.lastname IS NOT NULL")
->andWhere("p.function IS NOT NULL");
if ($extra_conditions!=null)
{
foreach ($extra_conditions as $condition)
{
#filter on firstname
if (key($condition)=='firstname')
$query = $query->andWhere('p.firstname LIKE ?1')
->setParameter(1, $condition['firstname']);
#filter on lastname
if (key($condition)=='lastname')
$query = $query->andWhere('p.lastname LIKE ?1')
->setParameter(1, $condition['lastname']);
#filter on gender
if (key($condition)=='gender')
$query = $query->andWhere('p.gender = '.$condition['gender']);
#filter on domain(s)
if (key($condition)=='domains')
$query = $query->andWhere('d.id IN ('.$condition['domains'].')');
#filter on town
if (key($condition)=='town')
$query = $query->andWhere('p.town LIKE ?1')
->setParameter(1, $condition['town']);
}
}
$query = $query->orderBy("p.lastname", "ASC");
$query = $qb->getQuery();
return $query->getResult();
}
There is no error, but whatever domains are given as search criteria; people from all domains are found and returned.
Domains are provided as an array like (2, 4).
What can I change to make it possible to find people belonging to certain domains?

Answer 1

After some trial-and-error I found two possible answers:
1) Apparently in the querybuilder you can refer to fields that live in join-tables, and are not actually part of an entity. Hence one solution would be:
#filter on domain(s)
if (key($condition)=='domains')
$query = $query->andWhere('p.domain_id IN ('.$condition['domains'].')');
...where domain_id lives in the join table "person_domain" created by Symfony2 unther the hood.
2) The inner join is now no longer needed. Using an inner join is possible as well, however it was written the wrong way and would not have worked anyway. It should have been written as:
->leftjoin('p:domain', 'd', 'ON p.id = d.id')
Hope that other people may benefit from the above.