Sonata Admin: Prevent a persist for a specific condition

Question

I am using sonata Admin. I have Two Entities: Vacation Entry + Employee Vacation Entry (1:m)

In my vacation entry admin class:

• The user selects employees (from the many to many relationship) to which I'd like to give the vacation.

• A validation is done over each employee through the Employee Vacation Entry entity.

  class VacationEntryAdmin extends Admin {
  
      // some 
      // content
      public function prePersist($cv)
      {
          // some 
          // content
          $validator = $this->getValidator();
          $errors = $validator->validate($employeeVacationEntry);
          if (count($errors) > 0) {
              foreach ($errors as $error) {
                  $errorsString = $error->getMessage();
                  $employeeName = $error->getRoot()->getEmployee()->getName();
                  $this->getRequest()->getSession()->getFlashBag()->add("danger", $employeeName . ': ' . $errorsString);
              }    //I'd like to stop the persistence of all the Vacation Entry here.
          }
          $em->persist($employeeVacationEntry);
      }
  
  }