Adding a one-to-one relationship with shared primary key can become a difficult task if the main table key is an auto-generated one.
Even the Hibernate Annotations documentation example only works with not auto-generated id, if you try to use an auto incremental id, for example,
it’s impossible to persist the 2 tables at the same time.
Surfing on the net I’ve seen some ppl with this kind of problem (I suppose one-to-one relationships are not so common, don’t know why) and most of ppl use the foreign-key approach that works ok but it’s not clean from my point of view, so I wanted to find a solution for my case.
The original example from the Hibernate Annotations Documentation is:
@Entity
public class Body {
@Id
public Long getId() { return id; }
@OneToOne(cascade = CascadeType.ALL)
@PrimaryKeyJoinColumn
public Heart getHeart() {
return heart;
}
…
}
@Entity
public class Heart {
@Id
public Long getId() { … }
}
As you can see this as not auto generated id and will not work just putting the @GeneratedValue annotation.
The final solution is:
@Entity
public class Body {
@Id
@GeneratedValue(strategy = IDENTITY)
public Long getId() { return id; }
@OneToOne(cascade = CascadeType.ALL)
@PrimaryKeyJoinColumn
public Heart getHeart() {
return heart;
}
…
}
@Entity
public class Heart {
@Id
@GeneratedValue(generator=”foreign”)
@GenericGenerator(name=”foreign”, strategy = “foreign”, parameters = {@Parameter(name=”property”, value=”body”)})
public Long getId() { …}
@OneToOne(mappedBy=”heart”)
public Body getBody() { … }
}
