How to access the join column (Foreign key) in Spring Data JPA without loading the mapped entity-CodePudding

I have a POST entiry and HeadingSlugEntity.

public class PostEntity implements Serializable {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer id;
    private String postId;
    private String uid;
    private String dateCreated;
    private String dateUpdated;

    @OneToOne(cascade = CascadeType.ALL, fetch = FetchType.LAZY)
    @JoinColumn(name = "headingSlugId", referencedColumnName = "headingSlugId")
    private HeadingSlugEntity headingSlugEntity;
}

I have a 1:1 mapping for HeadingSlugEntity. When I save post entity and headingSlugEntity together, headingSlugId is getting auto-populated. That is working fine. The next time when I fetch the post entity, I need to access the headingSlugId without getting the headingSlugEntity. (At this point of time, I don't need HeadingSlugEntity, I just need its ID.) I just need to get the headingSlugId. How to do it. Since this entity is not having the field headingSlugId, I can't set and get it. If I add a field named headingSlugId inside post entity, I will get hibernate duplicate field error. If I put

insertable = false, updatable = false)

and add field headingSlugId, the headingSlugId will be Null.

What basic stuff I am missing here ?

CodePudding user response：

You can map the foreign key to the entity twice in this case, one for actual ORM and another for getting the FK without actually firing a new query.

public class Answer {
   @Column(name = "headingSlugId", insertable = false, updatable = false)
   private Integer headingSlugId;

   @OneToOne(cascade = CascadeType.ALL, fetch = FetchType.LAZY)
   @JoinColumn(name = "headingSlugId", referencedColumnName = "headingSlugId")
   private HeadingSlugEntity headingSlugEntity;
}