UniqueFieldConstraint.php

<?php

namespace Drupal\Core\Validation\Plugin\Validation\Constraint;

use Drupal\Core\StringTranslation\TranslatableMarkup;
use Drupal\Core\Validation\Attribute\Constraint;
use Symfony\Component\Validator\Attribute\HasNamedArguments;
use Symfony\Component\Validator\Constraint as SymfonyConstraint;

/**
 * Checks if an entity field has a unique value.
 */
class UniqueFieldConstraint extends SymfonyConstraint {
  
  /**
   * This constraint is case-insensitive by default.
   *
   * For example "FOO" and "foo" would be considered as equivalent, and
   * validation of the constraint would fail.
   *
   * @var bool
   */
  public $caseSensitive = FALSE;
  public function __construct(mixed $options = NULL, ?bool $caseSensitive = NULL, public $message = 'A @entity_type with @field_name %value already exists.', ?array $groups = NULL, mixed $payload = NULL) {
    parent::__construct($options, $groups, $payload);
    $this->caseSensitive = $caseSensitive ?? $this->caseSensitive;
  }
  
  /**
   * {@inheritdoc}
   */
  public function validatedBy() : string {
    return '\\Drupal\\Core\\Validation\\Plugin\\Validation\\Constraint\\UniqueFieldValueValidator';
  }

}