Symfony2 - Many to Many relationship and LIMIT

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();
}