Symfony 2.8 : DQL query to display an arraycollection - doctrine-orm

Question

I'm a beginner on Symfony 2 and I have a problem with a DQL query : I'm trying to display a property that is an ArrayCollection.
Here's my case : Two classes joined together with a "ManyToOne" and "OneToMany"
DishGrade.php :
/**
* #var Dish $dish
*
* #ORM\ManyToOne(targetEntity="Dish", inversedBy="grades",
cascade={"persist", "remove", "merge"})
* #ORM\JoinColumn(name="dish_id", referencedColumnName="id", nullable=false)
*
*/
private $dish;
Dish.php :
/**
* #var \Doctrine\Common\Collections\Collection $grades
*
* #ORM\OneToMany(targetEntity="DishGrade", mappedBy="dish", cascade={"all"},
orphanRemoval=true)
*/
private $grades;
Then here's my controller which returns an array of objects "DishGrade"
/**
* Get grades dish.
*
*
* #ApiDoc(
* output = "Awadac\ApiBundle\Model\Dish",
* statusCodes = {
* 200 = "Returned when successful",
* 404 = "Returned when the dish is not found"
* }
* )
*
* #Get("/dishes/{id}")
*
* #param Request $request the request object
* #param int $id the dish id
*
* #return array
*
* #throws NotFoundHttpException when dish not exist
*/
public function getDishAction(Request $request, $id)
{
$dish = $this->getDishManager()->getRepository()->getGrades($id);
if (!$dish) {
throw $this->createNotFoundException('Dish does not exist.');
}
return $dish;
}
And here's my query that doesn't work :
DishRepository.php :
public function getGrades($id){
$qb = $this->_em->createQueryBuilder();
return $qb->select('d.grades')
->from('AwadacApiBundle:Dish', 'd')
->where('d.id = :id')
->setParameter('id', $id)
->getQuery()
->getResult();
}
the error code I get :
{"code":500,"message":"[Semantical Error] line 0, col 9 near 'grades FROM AwadacApiBundle:Dish': Error: Invalid PathExpression. Must be a StateFieldPathExpression.","errors":null}
And when I want to get all the properties from my object "Dish" it works, so I just wonder why I can't display this ArrayCollection alone.
Thank you for your time !

Answer 1

If you are already in the DishRepository you will be able to create the query builder by
$qb = $this->createQueryBuilder('d');
Further just remove the ->from() statement and I guess it should work properly:
return $qb->select('d.grades')
->where('d.id = :id')
->setParameter('id', $id)
->getQuery()
->getResult();