Why do I receive "This value should be of type string" when using a DateTime constraint on Symfony 5?

I have the following entity (only attached the relevant parts):

use ApiPlatform\Core\Annotation\ApiResource;
use Doctrine\ORM\Mapping as ORM;
use Symfony\Component\Validator\Constraints as Assert;

 * @ApiResource(mercure=true)
 * @ORM\Entity(repositoryClass="App\Repository\EventRepository")
class Event {
     * @ORM\Column(type="datetime")
     * @Assert\DateTime
     * @Assert\NotNull
    private $createdAt;

    public function __construct() {
        $this->createdAt = new \DateTime();

    public function getCreatedAt(): ?\DateTimeInterface {
        return $this->createdAt;

    public function setCreatedAt(\DateTimeInterface $createdAt): self {
        $this->createdAt = $createdAt;
        return $this;

Its repository:

class EventRepository extends ServiceEntityRepository {
    public function __construct(ManagerRegistry $registry) {
        parent::__construct($registry, Event::class);

When creating a POST request to the event endpoint (via Postman or the Swagger UI), it fails with the following exception:


Here is Solutions:

We have many solutions to this problem, But we recommend you to use the first solution because it is tested & true solution that will 100% work for you.

Solution 1

You are using the wrong of assertion.

Date expects a string or an object that can be cast into a string. And a DateTimeInterface is neither.

You should be using a Type constraint.

 * @Assert\Type("\DateTimeInterface")
 private $createdAt;

The ability to use Assert\Date to validate DateTime objects was deprecated on Symfony 4.2, and on Symfony 5.0 it was removed altogether.

Note: Use and implement solution 1 because this method fully tested our system.
Thank you 🙂

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0

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