Hibernate Unidirectional @ManyToMany

Question

I have a many-to-many relationship between accounts and groups. The data for the groups table comes pre-populated and there is no adding additional groups.

Using Hibernate, my desire is to:

1. Add an account to the account table,
2. Add a record to the account_group table, and
3. NOT add a record to the group table

It seems to me, no matter what I do, I always get a duplicate record in the group table. This is my problem. Here is my code:

Account.java

@Entity
@Table(name = "account", schema = "admin")
public class Account {

    @Id
    @GeneratedValue
    private UUID id;

...

    @ManyToMany(fetch = FetchType.EAGER, cascade = { CascadeType.PERSIST, CascadeType.MERGE })
    @JoinTable(name = "account_grouping", schema = "admin", joinColumns = @JoinColumn(name = "account_id"), inverseJoinColumns = @JoinColumn(name = "grouping_id"))
    private Set<Grouping> groupings;

...

    // getters and setters

}

Grouping.java

@Entity
@Table(name = "grouping", schema = "admin")
public class Grouping {

...

    @Id
    @GeneratedValue
    private UUID id;

...

    // getters and setters

}

AccountDao.java

@Repository
public class AccountDao extends AbstractJpaDao<Account, String> {

...

    @Transactional
    public boolean create(Account newAccount) {
        try {
            getEntityManager().merge(newAccount);
            return true;
        } catch(Exception e) {
            System.out.println("Danger, Will Robinson!: " + e);
            return false;
        }
    }

}

I have looked up many questions and websites regarding Hibernate @ManyToMany examples, but I must be missing something. Thank you for reading and for your help.

Answer 1

Unfortunately I do not have enough rep to make a comment, so I'll throw my guess as an answer. Make sure the Group entity has an ID when selecting a Group for your Account before saving your entity. Otherwise the Group entity is treated as a new Object and will be saved into the grouping table.