hibernate optional join - need to return join column value either way

Question

as a follow on from hibernate optional join

Many existing queries in the system rely on there being a mapped relationship between EntityOne and EntityTwo and changing this is not an attactive option, however I now need to start storing and retrieving values in tbl_one.two_id which do not exist in the joined table. On the way in, this works fine with the following mapping:

@Entity
@Table(name="tbl_one")
public class EntityOne
{
    ....
    @ManyToOne
    @NotFound(action = NotFoundAction.IGNORE)
    @JoinColumn(name = "two_id")
    private EntityTwo two;
    ....
}

.. However when querying, if a result has a value for two_id which does not exist in the joined table, the value for the field two is null and I have no way of telling what the value for tbl_one.two_id actually is. I was hoping hibernate would create a dummy EntityTwo object and populate it's id field only if the relationship did not exist.

I've also tried mapping two_id to another field without a join:

@Entity
@Table(name="tbl_one")
public class EntityOne
{
    ....
    @ManyToOne
    @NotFound(action = NotFoundAction.IGNORE)
    @JoinColumn(name = "two_id", insertable = false, updatable = false)
    private EntityTwo two;

    @Column(name = "two_id")
    private String twoId;
    ....
}

... but then the two field is never populated, even when the corresponding record exists.

Essentially I need some way of inserting/updating a value for tbl_one.two_id and retrieving a joined entity for EntityTwo if the relationship exists, or just the value for tbl_one.two_id if the relationship does not exist.

I'm hoping to be able to solve this without creating two mappings for the same table.

thanks.

EDIT: more info

public class EntityTwo
{
    ...
    @Id
    @Column(name = "site_id")
    private String id;
    ...
}

Answer 1

This should work :

@ManyToOne
@NotFound(action = NotFoundAction.IGNORE)
@JoinColumn(name = "two_id", insertable = false, updatable = false)
private EntityTwo two;

@Formula("two_id")
private String twoId;

Hibernate will select the two_id column twice : once to populate the two relationship, and once to populate the twoId. The twoId property is read-only, though.

You could also do the reverse, but then it's the two property which will become read-only:

@ManyToOne
@NotFound(action = NotFoundAction.IGNORE)
@JoinFormula("two_id")
private EntityTwo two;

@Column("two_id")
private String twoId;