Hibernate save entity with existing Id

Question

I am creating a CRUD application using Servlets and Hibernate.

When I try to save a new entity using save(), then Hibernate executes the SQL Update query and not Insert. The entity already contains the generated Id (UUID) and as I understand it, it searches for this entity in the database (h2 in-memory) and does not find it. How to properly save an entity in the database if the id has already been generated.

@Entity
@Table(name = "MATCH")
public class Match implements Serializable {
    @Id
    @Column(name = "MATCH_ID")
    private UUID id;

    @ManyToOne
    private Player playerOne;

    @ManyToOne
    private Player playerTwo;

    @ManyToOne
    private Player winner;


    @Transient
    private int[] score = new int[2];

    public Match() {

    }

        //getters and setters
}




   public void executePost(HttpServletRequest servletRequest, HttpServletResponse servletResponse) throws ServletException, IOException {
        Transaction transaction = null;
        try (Session session = DBHandler.getSessionFactory().openSession()) {
            transaction = session.beginTransaction();

            UUID MatchUuid = UUID.fromString(servletRequest.getParameter("match-uuid"));  
            currentMatchService = CurrentMatchService.getInstance(); //service stores current matches in the app's memory
            currentMatch = currentMatchService.getMatch(MatchUuid);
            currentMatch.setWinner(currentMatch.getPlayerOne()); //player One set like winner just for test
            session.save(currentMatch);
            transaction.commit();
        } catch (Exception e) {
            if (transaction != null) {
                transaction.rollback();
            }
            e.printStackTrace();
        }

Answer 1

As I understand the question you want to persist the entity in the database without letting Hibernate generate an identifier for you. To accomplish it you can use following code:

If the entity with the id already exists in the database and should be updated - please use:

session.merge(myEntity); // myEntity contains the id

If it's a new entity and should be inserted - please use:

UUUID id = UUID.randomUUID(); // new id will be generated
myEntity.setId(id);
session.persist(myEntity);