Symfony6 Form Render Object of class App\Entity\User could not be converted to string

I am trying to render form of Team entity which is attached to User with ManyToOne relationship. See below Entity Class:

<?php

namespace App\Entity;

class Team
{
    #[ORM\Id]
    #[ORM\GeneratedValue]
    #[ORM\Column]
    private ?int $id = null;

    #[ORM\ManyToOne(inversedBy: 'teams')]
    #[ORM\JoinColumn(nullable: false)]
    private ?User $owner = null;
...

Below is User entity class code:

<?php

namespace App\Entity;

Class User {

    #[ORM\OneToMany(mappedBy: 'owner', targetEntity: Team::class)]
    private Collection $teams;
....

Here is the controller class code where I am rending form view:

<?php

namespace App\Controller;

class TeamController extends AbstractController
{
    #[Route('/new', name: 'app_team_new', methods: ['GET', 'POST'])]
    public function new(Request $request, TeamRepository $teamRepository): Response
    {
        $team = new Team();
        $form = $this->createForm(TeamType::class, $team);
        $form->handleRequest($request);

        if ($form->isSubmitted() && $form->isValid()) {
            $teamRepository->save($team, true);

            return $this->redirectToRoute('app_team_index', [], Response::HTTP_SEE_OTHER);
        }

        return $this->render('team/new.html.twig', [
            'team' => $team,
            'form' => $form,
        ]);
    }
...

And here is the TeamType form class

<?php

namespace App\Form;


class TeamType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options): void
    {
        $builder
            ->add('name')
            ->add('intro')
            ->add('country')
            ->add('balance')
            ->add('created_at')
            ->add('updated_at')
            ->add('owner')
        ;
    }

    public function configureOptions(OptionsResolver $resolver): void
    {
        $resolver->setDefaults([
            'data_class' => Team::class,
        ]);
    }
}
...

And lastly, the team/new.html.twig

{% extends 'layouts/base.html.twig' %}

{% block title %}
	New Team
{% endblock %}

{% block body %}
	<main class="container form-signin w-100 m-auto">
		<h1>Add Team</h1>

		{{ form_start(form) }}
		{{ form_widget(form) }}
		<button class="btn">{{ button_label|default('Save') }}</button>
		{{ form_end(form) }}


		<a href="{{ path('app_team_index') }}" class="btn btn-link bi bi-arrow-left text-decoration-none">
			  Back to all teams</a>
	</main>
{% endblock %}

I am getting an error that Object of class App\Entity\User could not be converted to string exactly near the line 'form' => $form,.

What could be a possible issue?

I found the solution. If you want to use an entity as a form field, you need to specify the class and the choice_label options in your form type. The class option tells Symfony which entity class to use for the field, and the choice_label option tells Symfony which property or method to use as the label for each choice. To fix this, you need to configure your form type for the User field like this:

<?php

namespace App\Form;

use App\Entity\Team;
use App\Entity\User;
use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\OptionsResolver\OptionsResolver;
use Symfony\Bridge\Doctrine\Form\Type\EntityType;


class TeamType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options): void
    {
        $builder
            ->add('name')
            ->add('intro')
            ->add('country')
            ->add('balance')
            ->add('created_at')
            ->add('updated_at')
            ->add('owner', EntityType::class, [
                'class' => User::class,
                'choice_label' => 'full_name', // or any other property or method that returns a string
            ]);
        ;
    }
...

Hope this help someone.

When doctrine tries to display relationships, in your case the Team and User classes. depending on the side of the relationship, doctrine tries to convert these classes to a string, in order to display select with option choice value in html form. You should be to implement __toString methods

class User
{
  //...
  public function __toString()
  {
    return (string) $this->getUserIdentifier();
  }
}

class Team
{
  //...
  public function __toString()
  {
    return (string) $this->name;
  }
}

If the form will only be used to add new Teams to the current User, then you should not include the owner field in the form. Instead, manually set the owner to the current User in the Controller.

So omit the ->add('owner', /*...*/); call from your FormType and edit your handler to be something like the following (adjust for your specific Entity methods' logic):

    public function new(Request $request, TeamRepository $teamRepository): Response
    {
        $team = new Team();
        $user = $this->getUser();
        $user->addTeam($team);
        $team->setOwner($user);

        /* create form and handle Request */
    }

As an alternative to setting the owner in the handler, and especially since the owner is not nullable, you could set the owner in the Team constructor. You would then create a Team by passing the current User.