Is there a way to pass detached object to JPA persist? (detached entity passed to persist)

Question

I have 2 entities : Account and AccountRole.

public class Account {
   private AccountRole accountRole;

   @ManyToOne(cascade = CascadeType.PERSIST, fetch = FetchType.EAGER)
   public AccountRole getAccountRole() {
      return accountRole;
   }

.

public class AccountRole {
    private Collection<Account> accounts = new ArrayList<Account>();

    @OneToMany(mappedBy = "accountRole", fetch = FetchType.EAGER)
    public Collection<Account> getAccounts() {
         return accounts;
    }

Problem comes when I take the accountRole from database and try to persist my Account. At this point I just created my account and role already exists in db.

AccountRole role = accountService.getRoleFromDatabase(AccountRoles.ROLE_USER);
account.setAccountRole(role);

//setting both ways, as suggested
public void setAccountRole(AccountRole accountRole) {
    accountRole.addAccount(this);
    this.accountRole = accountRole;
}

entityManager.persist(account); // finally in my DAO

I read this : JPA/Hibernate: detached entity passed to persist And what I understood, I must set the entities values from both direction, so that what I am doing in my setter.

Still getting error.

 org.hibernate.PersistentObjectException: detached entity passed to persist: foo.bar.pojo.AccountRole

Answer 1

Just replace the

entityManager.persist(account);

with:

entityManager.merge(account);

And allow merge cascading:

@ManyToOne(cascade = { CascadeType.PERSIST, CascadeType.MERGE }, fetch = FetchType.EAGER)
public AccountRole getAccountRole() {
    return accountRole;
}

Because merge does this:

If your entity is new, it's the same as a persist(). But if your entity already exists, it will update it.

Answer 2

It looks like you leave the transaction during your processing, so the accountRole gets detached, or it is already detached for other reasons.

A call to entityManager.merge(accountRole) before calling entityManager.persist(account) should fix it.

EDIT: Unfortunately, if you cannot be sure if the accountRole already exists in the DB, you will have to check it by querying. If it exists - merge, if not - persist. It is indeed a hassle, but I have not yet seen a better workaround.

EDIT2: The entity you pass to the merge method will remain detached - the managed entity will be returned by the merge, so you would need to merge first, then set the reference on the account to the return value of the merge.