@RequestMapping(value = "/addComment/{topicId}", method = RequestMethod.POST)
        public String saveComment(@PathVariable int topicId, @ModelAttribute("newComment")Comment comment, BindingResult result, Model model){
			Topic commentedTopic = topicService.findTopicByID(topicId);
			commentedTopic.addComment(comment);
			
			// TODO: Add a validator here
			if (!comment.isValid() ){
				return "//";
				
            }
			// Go to the "Show topic" page
			commentService.saveComment(comment);
			
            return "redirect:../details/" + topicService.saveTopic(commentedTopic);

        }

@Service
@Transactional
public class CommentService {

	@Autowired
	private CommentRepository commentRepository;
	
	public int saveComment(Comment comment){
		return commentRepository.save(comment).getId();
		
	}	

}

@Service
@Transactional
public class TopicService {
	@Autowired
	private TopicRepository topicRepository;
	
	public int saveTopic(Topic topic){
		return topicRepository.save(topic).getId();

	}
}

@Entity
@Table(name = "T_TOPIC")
public class Topic {
	
	@Id
	@GeneratedValue(strategy=GenerationType.AUTO)
	private int id;
	
	@ManyToOne
	@JoinColumn(name="USER_ID")
	private User author;
	
	@Enumerated(EnumType.STRING)	
	private Tag topicTag;
	
	private String name;
	private String text;
}

@Entity
@Table(name = "T_COMMENT")
public class Comment
{
	@Id
	@GeneratedValue(strategy=GenerationType.AUTO)
    private int id;
	
	@ManyToOne
	@JoinColumn(name="TOPIC_ID")
	private Topic topic;
    
	@ManyToOne
	@JoinColumn(name="USER_ID")
    private User author;

    private String text;
    private Date creationDate;
}