symfony2 doctrine2: addselect elements to existing entity - performance

Question

I am using Symfony2 and Doctrine2.
There are many instances when I have an entity and I need to loop through its associated entities. Of course it often triggers new queries and is not very performant.
Would there be a best practice to addselect other entities to an existing one?
Think about when you use a paramconverter in symfony. It just gets you the entity. What if I retrieve an order and want to loop through its orderLines? Do I need to build a new query and retrieve->leftjoin('order.orderlines', 'l')->addselect('l')->where('order = $order') ?

Answer 1

The best practice in this case is to use a custom repository method that explicitly joins the associated entity. Then Doctrine will not have to query individually through every iteration of the loop. You can also use this custom repository method in the ParamConverter.
Custom Repository Method:
Here's an example Controller:
use Sensio\Bundle\FrameworkExtraBundle\Configuration\Route;
use Sensio\Bundle\FrameworkExtraBundle\Configuration\ParamConverter;
/**
* #Route("/blog/{id}")
* #ParamConverter("post", class="MyBundle:Order",
options={"repository_method" = "findOrderWithLineItems"})
*/
public function showAction(Order $order)
{
}
Then specifying the custom repository on the entity:
namespace MyBundle\Entity;
use Doctrine\ORM\Mapping as ORM;
/**
* #ORM\Entity(repositoryClass="MyBundle\Entity\OrderRepository")
*/
class Order
{
}
Then your custom repository:
namespace MyBundle\Entity;
use Doctrine\ORM\EntityRepository;
class OrderRepository extends EntityRepository
{
public function findOrderWithLineItems($id)
{
return $this->createQueryBuilder('o')
->join('o.orderLines', 'ol')
->where('o.id = :id')
->setParameter('id', $id)
->getQuery()
->getResult()
;
}
}
Always Join via Eager Fetching:
If instead you want to always fetch the associated entity (always join the table), even when doing a simple select on the base entity, you can specify an eager join on the associated entity:
class Order
{
/**
* #ManyToOne(targetEntity="OrderLines", fetch="EAGER")
*/
private $orderLines;
}