@Override
  @Transactional
  @PreAuthorize("hasRole('ROLE_ADMIN')")
  public void remove(Long id) throws IllegalArgumentException {
    Category category = categoryRepository.findOne(id);
    if (category == null) {
      throw new IllegalArgumentException(String.format("Category with id=%d does not exist.", id));
    }
    /*List<Question> questions = questionRepository.findByCategory(category);

    for (Question question : questions) {
    	question.setCategory(null);
    	questionRepository.save(question);
    }*/
    categoryRepository.delete(id);
  }
 @Override
 public Category findOne(Long id) {
   return categoryRepository.findOne(id);
 }