Doctrine: how to add exception for UniqueEntity?

Question

symfony

There is a questionnaire. The completed form is saved in Answer.
Limited duplication $userand $questionusing UniqueEntity.
There is a property $file. If it's not null, then UniqueEntity should be avoided and duplication allowed. Or specify $questionan id that should not be subject to the duplication restriction.
How to add such exception for UniqueEntity? Other offers?

<?php
namespace App\Entity;
use Doctrine\Common\Collections\ArrayCollection;
use Doctrine\Common\Collections\Collection;
use Doctrine\ORM\Mapping as ORM;
use Symfony\Bridge\Doctrine\Validator\Constraints\UniqueEntity;

/**
 * @UniqueEntity({"user", "question"});
 * @ORM\Entity(repositoryClass="App\Repository\AnswerRepository")
 */
class Answer
{
    /**
     * @ORM\Id()
     * @ORM\GeneratedValue()
     * @ORM\Column(type="integer")
     */
    private $id;

    /**
     * @ORM\ManyToOne(targetEntity="App\Entity\User", inversedBy="answers")
     * @ORM\JoinColumn(nullable=false)
     */
    private $user;

    /**
     * @ORM\ManyToOne(targetEntity="App\Entity\Question", inversedBy="answers")
     */
    private $question;

    /**
     * @ORM\Column(type="string", length=255, nullable=true)
     */
    private $file;

    public function getId(): ?int
    {
        return $this->id;
    }

    public function getUser(): ?user
    {
        return $this->user;
    }

    public function setUser(user $user): self
    {
        $this->user = $user;

        return $this;
    }

    public function getQuestion(): ?question
    {
        return $this->question;
    }

    public function setQuestion(?question $question): self
    {
        $this->question = $question;

        return $this;
    }

    public function getFile()
    {
        return $this->file;
    }

    public function setFile($file): self
    {
        $this->file = $file;

        return $this;
    }
}

Answer 1

Do not use UniqueEntity, but directly validate $request itself and already there dance from various conditions. If you work with the validator correctly, then it will not skip the constraints that you specify.