Api Platform : order on an entity cascade - symfony

Question

With Api Platform, we can order by association.
Documentation :
use ApiPlatform\Core\Annotation\ApiResource;
/**
* #ApiResource(attributes={"order"={"author.username"}})
*/
class Book
{
...
But I want to order on an entity cascade.
For the example below I tested this with this error :
* #ApiResource(
* attributes={
* "order"={"exercises.repetitions.id":"asc"}
* }
* )
[Semantical Error] line 0, col 422 near 'id ASC, rests_a6.id': Error: Class App\Entity\TrainingSerieExercise has no field or association named repetitions.id
TrainingSerie entity :
* #ApiResource(
...
* attributes={
* "order"={"exercises.repetitions.id":"asc"}
* }
* )
*/
class TrainingSerie
{
...
/**
* #var TrainingSerieExercise[]|ArrayCollection
*
* #ORM\OneToMany(
* targetEntity="App\Entity\TrainingSerieExercise",
* mappedBy="serie",
* cascade={"persist"}
* )
* #Groups({
* "trainings_read",
* "training_series_read",
* "training_series_write",
* })
*/
private $exercises;
...
TrainingSerieExercise entity :
...
class TrainingSerieExercise
{
...
/**
* #var TrainingSerieRepetition[]|ArrayCollection
*
* #ORM\OneToMany(
* targetEntity="App\Entity\TrainingSerieExerciseRepetition",
* mappedBy="exercise",
* cascade={"persist"},
* )
* #Groups({
* "training_series_read",
* "training_series_write",
* "training_serie_exercices_write",
* })
*/
private $repetitions;
...
TrainingSerieExerciseRepetition entity :
class TrainingSerieExerciseRepetition
{
...
/**
* #var integer
*
* #ORM\Id
* #ORM\Column(name="id", type="integer")
* #ORM\GeneratedValue(strategy="AUTO")
* #Groups({
* "training_series_read",
* })
*/
private $id;
...

Answer 1

Following this Doctrine doc this will order TrainingSerieExercise::$repetitions by id:
class TrainingSerieExercise
{
...
/**
* #var TrainingSerieRepetition[]|ArrayCollection
*
* #ORM\OneToMany(
* targetEntity="App\Entity\TrainingSerieExerciseRepetition",
* mappedBy="exercise",
* cascade={"persist"},
* )
* #ORM\OrderBy({"id" = "ASC"})
* #Groups({
* "training_series_read",
* "training_series_write",
* "training_serie_exercices_write",
* })
*/
private $repetitions;
...