Symfony2 - Many to Many relationship and LIMIT - symfony

Question

Im use many-to-many relationship;
User entity;
/**
* #ORM\ManyToMany(targetEntity="Conversation", inversedBy="users")
*/
protected $conversations;
Conversation entity;
/**
* #ORM\ManyToMany(targetEntity="User", mappedBy="conversations")
* #ORM\JoinTable(name="user_conversation")
*/
protected $users;
When, I work this function;
$user->getConversations();
Symfony work this sql code in background;
SELECT
t0.id AS id1,
t0.conversationid AS conversationid2
FROM
Conversation t0
INNER JOIN user_conversation ON t0.id = user_conversation.conversation_id
WHERE
user_conversation.user_id = ?
And select all conversation. This will be performance problem. So, I work with repository class. But, I can't work many-to-many and limit function with together. What should I do? What I write to repository class?

Answer 1

If you want to optimize access to large collections in doctrine just use Criteria (That only works on OneToMany associations.)
Example:
use Doctrine\ORM\Mapping as ORM;
use Doctrine\Common\Collections\Criteria;
/**
* #ORM\Entity
* #ORM\Table
*/
class User
{
....
public function getLatestConversation()
{
$criteria = Criteria::create()
->setMaxResults(10);
return $this->conversations->matching($criteria);
}
}
For ManyToMany I think you must create a custom query:
public function getLatestConversations($user)
{
$qb = $this->createQueryBuilder("c");
$qb
->leftjoin("c.users", "u")
->where("u = :user")
->setParameter("user", $user)
->setMaxResults(2);
return $qb->getQuery()->getResult();
}

Answer 2

You can convert it to Arraycollection Object:
$input = $repo->getConversations(); //manytomany relation
$arr = new ArrayCollection();
foreach ($input as $e){
$arr->add($e);
}
And then use your Criteria on $arr

Answer 3

Try
$repository = $em->getRepository('YourBundle:Conversations');
$query = $repository->createQueryBuilder('C')
->join('C.Users', 'U')
->where('U.id = :uid')
->setMaxResults(20) //set your amount for limit
->setParameter('uid', $user_id)
->getQuery();
$result = $query->getResults();