Say I have a unidirectional @ManyToOne relationship like the following:

    @Entity
    @Table(name = "TestUser")
    @AllArgsConstructor
    @NoArgsConstructor
    @Getter
    @Setter
    public class TestUser {
    
        @Id
        @Column(nullable = false)
        private String id;
    
        @Column(name = "some_property")
        private String someProperty;
    
        @Override
        public boolean equals(Object o) {
            if (this == o) return true;
            if (!(o instanceof TestUser)) return false;
            return id != null && id.equals(((TestUser) o).getId());
        }
    
        @Override
        public int hashCode() {
            return getClass().hashCode();
        }
    }
    
    @Entity
    @Setter
    @Getter
    @NoArgsConstructor
    @AllArgsConstructor
    public class BugTicket {
    
        @Id
        @GeneratedValue
        @Column(name = "id", nullable = false)
        private Long id;
    
        @ManyToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
        @JoinColumn
        private TestUser testUser;
    
        public BugTicket(TestUser testUser) {
            this.testUser = testUser;
        }
    }
    
    class Driver {
    
        public void run(String... args) throws Exception {
            TestUser u1 = new TestUser("user-id-1", "value1");
            userRepository.save(u1);
    
            var ticket = new BugTicket(u1);
            ticketRepository.save(ticket);
    
            ticket.getTestUser().setSomeProperty("value2");
            ticketRepository.save(ticket);
        }
    }

I want to update the user entity's 'someProperty' whenever I update BugTicket entity. Hence I added CascadeType.ALL to BugTicket's user.

However, when save is called, hibernate tries to create a new user and throws exception

    Hibernate: insert into test_user (some_property, id) values (?, ?)
    2022-10-02 18:33:39.404  WARN 30632 --- [  restartedMain] o.h.engine.jdbc.spi.SqlExceptionHelper   : SQL Error: 0, SQLState: 23505
    2022-10-02 18:33:39.405 ERROR 30632 --- [  restartedMain] o.h.engine.jdbc.spi.SqlExceptionHelper   : ERROR: duplicate key value violates unique constraint "test_user_pkey"
      Detail: Key (id)=(user-id-1) already exists.

Why does hibernate try to insert User once again? Is removing CascadeType.all from BugTicket, and explicitely saving user ' ticket.getTestUser().setSomeProperty("value2");' the only way?

CodePudding user response：

When you save an entity with jparepository it returns the persisted user so you need to use that

CodePudding user response：

When you try to save your "ticket", ticket.getTestUser() is detached so Hibernate will try to create it. You need to work inside a transaction.