Symfony 5 - Using DataTransformer on Entity with another column than primary key

Following this doc https://symfony.com/doc/current/form/data_transformers.html#harder-example-transforming-an-issue-number-into-an-issue-entity, we learn how to fill a field (which is an Entity) without using a choice field type or similar.

It seems to work, using the primary key of the Entity concerned (el famoso "id").

However, i want to use another field and store it in a table, but i have an error (see screeshot at bottom)

Entities :

<?php

namespace App\Entity;

use App\Repository\LandRepository;
use Doctrine\Common\Collections\ArrayCollection;
use Doctrine\Common\Collections\Collection;
use Doctrine\ORM\Mapping as ORM;

/**
    * @ORM\Entity(repositoryClass=LandRepository::class)
    * @ORM\Table(name="land",indexes={@ORM\Index(columns={"uid"})})
    * @ORM\HasLifecycleCallbacks()
*/
class Land
{   
    /**
        * @ORM\Id()
        * @ORM\GeneratedValue()
        * @ORM\Column(type="integer")
    */
    private $id;
    
    /**
        * @ORM\Column(type="string", length=255)
    */
    private $libelle;
    
    /**
        * @ORM\Column(type="integer")
    */
    private $uid;   
    
    
    public function getId(): ?int
    {
        return $this->id;
    }
    
    public function getLibelle(): ?string
    {
        return $this->libelle;
    }
    
    public function setLibelle(string $libelle): self
    {
        $this->libelle = $libelle;
        
        return $this;
    }
    
    public function getUid(): ?int
    {
        return $this->uid;
    }
    
    public function setUid(int $uid): self
    {
        $this->uid = $uid;
        
        return $this;
    }
    
}



namespace App\Entity;

use App\Repository\RideRepository;
use Doctrine\ORM\Mapping as ORM;

/**
    * @ORM\Entity(repositoryClass=RideRepository::class)
    * @ORM\HasLifecycleCallbacks()
*/
class Ride
{   
    /**
        * @ORM\Id()
        * @ORM\GeneratedValue()
        * @ORM\Column(type="integer")
    */
    private $id;
    
    /**
        * @ORM\Column(type="string", length=255)
    */
    private $libelle;
    
    /**
        * @ORM\ManyToOne(targetEntity=Land::class)
        * @ORM\JoinColumn(name="areaparent", referencedColumnName="uid")
    */
    private $areaparent;
    
    
    public function getId(): ?int
    {
        return $this->id;
    }
    
    public function getLibelle(): ?string
    {
        return $this->libelle;
    }
    
    public function setLibelle(string $libelle): self
    {
        $this->libelle = $libelle;
        
        return $this;
    }
    
    public function getAreaparent(): ?Land
    {
        return $this->areaparent;
    }
    
    public function setAreaparent(?Land $areaparent): self
    {
        $this->areaparent = $areaparent;
        
        return $this;
    }
    
}

Expected final result :

"Land" table

"Ride" table

So you can see that in the "ride" table that the "areaparent" column is relative to the "land.uid" column.

"Land" form is classic

"Ride" form have a minor change : The "areaparent" is not a choice field, it's a text type which will call my DataTransformer

Extract of my form "RideType"

<?php
    
    namespace App\Form;
    
    use App\Entity\Ride;
    use App\Entity\Land;
    use Symfony\Component\Form\AbstractType;
    use Symfony\Bridge\Doctrine\Form\Type\EntityType;
    use Symfony\Component\Form\FormBuilderInterface;
    use Symfony\Component\OptionsResolver\OptionsResolver;
    use App\Repository\LandRepository;
    use Symfony\Component\Form\Extension\Core\Type\TextType;
    use App\Form\DataTransformer\UIDTransformer;
    
    class RideType extends AbstractType
    {
    
        private $transformer;

        public function __construct(UIDTransformer $transformer)
        {
            $this->transformer = $transformer;
        }       
        public function buildForm(FormBuilderInterface $builder, array $options)
        {
            $builder
            ->add('libelle')
            ->add('areaparent', TextType::class, [
                'invalid_message' => 'That is not a valid areaparent number',
            ])
            ;
            
            $builder->get('areaparent')->addModelTransformer($this->transformer);   
        }
        
        public function configureOptions(OptionsResolver $resolver)
        {
            $resolver->setDefaults([
            'data_class' => Ride::class,
            ]);
        }
    }

Extract of my DataTransformer :

<?php
    namespace App\Form\DataTransformer;
    
    use App\Entity\Land;
    use Doctrine\ORM\EntityManagerInterface;
    use Symfony\Component\Form\DataTransformerInterface;
    use Symfony\Component\Form\Exception\TransformationFailedException;
    
    class UIDTransformer implements DataTransformerInterface
    {
        private $entityManager;
        
        public function __construct(EntityManagerInterface $entityManager)
        {
            $this->entityManager = $entityManager;
        }
        
        /**
            * Transforms an object (Land) to a string (areaparent).
            *
            * @param  Land|null $Land
            * @return string
        */
        public function transform($land)
        {
            if (null === $land) {
                return '';
            }
            
            return $land->getUid();
        }
        
        /**
            * Transforms a string (police) to an object (Land).
            *
            * @param  string $areaparent
            * @return Land|null
            * @throws TransformationFailedException if object (Land) is not found.
        */
        public function reverseTransform($areaparent)
        {
            // no areaparent? It's optional, so that's ok
            if (!$areaparent) {
                return;
            }
            
            $land = $this->entityManager->getRepository(Land::class)->findByUid($areaparent);
            if (count($land) == 0) {
                // causes a validation error
                // this message is not shown to the user
                // see the invalid_message option
                throw new TransformationFailedException(sprintf('Land with areaparent "%s" does not exist!',$areaparent));
            }
            return $land[0];
        }
    }           

Error

I try to debug the symfony/doctrine code, and if i correctly understand, the error appears because the field "uid" is not considered as an "identifier".

See some dump.

Have you got some ideas ?

Thanks !