JPA Hibernate Composite Key as Foreign Key Parent / Child saving

Question

i am currently facing a problem within my application and would highly appreciate if somebody has an idea how to solve it.

I have two DB Tables

Item
--------------
OrderID
Status

Detail
---------------
OrderId
Status
Price

Within my app i have two entities

@Entity
@Table(name = "Item")
@IdClass(ItemKey.class)
public class Item {

@Column(name="OrderId")
private String orderId

@Column(name="Status")
private String status

@OneToOne
@JoinColumn(name="OrderId", referencedColumnName="OrderId")
@JoinColumn(name="Status", referencedColumnName="Status")
private Detail detail

}

And the second Entity

@Entity
@Table(name = "Detail")
@IdClass(ItemKey.class)
public class Detail{

@Column(name="OrderId")
private String orderId

@Column(name"Status")
private String status

@Column(name"Price")
private double price

}

I have in the DB a Forgein Key (OrderId, Status) referring from Details to Item Table. Now i have the issue if i am trying to create a Object: Item including a nested Object Detail and trying to save them via the ItemRepository i am getting an error message that related key is not available.

Reason i guess is that internally Hibernate saves first the child and then the parent, so no key would be available at that time.

I could manage to fix the problem by adding in the Entity: Detaila bi-directional mapping and added in Items the mappedBy argument in the @OneToOne Annotation. Unfortunately i dont like the solution because then i would have the attribute always on the Detail Entity which isnt really required and needed.

Does anybody has an idea how to get this working via a unidirectional relation. i tried already @MapsId and @PrimaryKeyColumnJoin but same result.

Answer 1

You would have to show us the code you use for persisting, but maybe you are calling entityManager.persist(detail) before entityManager.persist(item) ? Hibernate does not konw about the ordering. Anyway, I would suggest you use embedded ids instead as id class support has some rough edges.

@Entity
@Table(name = "Item")
public class Item {

  @EmbeddedId
  private ItemId id = new ItemId();

  @OneToOne(mappedBy = "item")
  private Detail detail;

}

@Embeddable
public class ItemId {

  @Column(name = "OrderId")
  private String orderId;

  @Column(name = "Status")
  private String status;

}

@Entity
@Table(name = "Detail")
public class Detail{

  @OneToOne
  private Item item;

  @Column(name = "Price")
  private double price;

}