class UniqueFieldConstraint

class UniqueFieldConstraint extends SymfonyConstraint {
  public $message = 'A @entity_type with @field_name %value already exists.';
  
  /**
   * 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;
  
  /**
   * Returns the name of the class that validates this constraint.
   *
   * @return string
   */
  public function validatedBy() {
    return '\\Drupal\\Core\\Validation\\Plugin\\Validation\\Constraint\\UniqueFieldValueValidator';
  }

}