EasyAdmin convert value - php

Question

For work I need to read through Symfony 5: The Fast Track. But in chapter 9 I have some problems. I have two entities Conference and Comment. The Comment entity is connected with the ID of the Conference.
Comment:
/**
* #ORM\ManyToOne(targetEntity=Conference::class, inversedBy="comments")
* #ORM\JoinColumn(nullable=false)
*/
private $conference;
public function setCreatedAt(\DateTimeInterface $createdAt): self
{
$this->createdAt = $createdAt;
return $this;
}
public function getConference(): ?Conference
{
return $this->conference;
}
My EasyAdminController looks like this:
public function configureMenuItems(): iterable
{
return [
MenuItem::linkToCrud('Conference', '', Conference::class),
MenuItem::linkToCrud('Comment', '', Comment::class)>setController(CommentCrudController::class),
];
}
And the CommentCrudController likt that:
public function configureFields(string $pageName): iterable
{
return [
TextField::new('author'),
TextEditorField::new('text'),
TextField::new('email'),
DateTimeField::new('createdAt'),
IdField::new('conference')->formatValue(function ($value) {
dd($value);
}),
TextField::new('photoFilename'),
];
}
So first my problem is that I need values as a object of Conference. Because I don't know how to do it right I tried to use formatValue but the dd($value)is never executed. Can someone help me with that problem or link me somewhere where I can find the answer.
Thank you in advantage.