Symfony, constraint for User

Good day! Just started learning Symfony on my own.

I’m making a news portal. The administrator can download news from an Excel file. I am converting a file to an associative array. For example:

[ 'Title' => 'Some title',
  'Text'  => 'Some text',
  'User'  => '[email protected]',
  'Image' => 'https://loremflickr.com/640/360'
]

Next, I want to send this array to the form and use ‘constraints’ to validate it.
There are no problems with the fields ‘Title’, ‘Text’, ‘Image’. I don’t know how to properly check the ‘User’ field. The user in the file is submitting an Email, but I want to check that a user with that Email exists in the database.

NewsImportType

    class NewsImportType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->add('title', TextType::class, [
                'constraints' =>
                [
                    new NotBlank(),
                    new Length(['min' => 256])
                ],
            ])
            ->add('text', TextareaType::class, [
                'constraints' =>
                [
                    new NotBlank(),
                    new Length(['max' => 1000])
                ],
            ])
            ->add('user', TextType::class, [
                'constraints' =>
                [
                    new NotBlank(),
                    new Email(),
                ],
            ->add('image', TextType::class, [
                'constraints' =>
                [
                    new NotBlank(),
                    new Length(['max' => 256]),
                    new Url()
                ],
            ]);
    }

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

The entities User and News are connected by a One-to-Many relationship.

I was thinking about using ChoiceType and calling UserRepository somehow, but I don’t understand how to apply it correctly.

Please tell me how to correctly write ‘constraint’ for the ‘user’ field.
thank!