How can I make a JPA OneToOne relation lazy

Question

In this application we are developing, we noticed that a view was particularly slow. I profiled the view and noticed that there was one query executed by hibernate which too

Answer 1

As I explained in this article, unless you are using Bytecode Enhancement, you cannot fetch lazily the parent-side @OneToOne association.

However, most often, you don't even need the parent-side association if you use @MapsId on the client side:

@Entity(name = "PostDetails")
@Table(name = "post_details")
public class PostDetails {

    @Id
    private Long id;

    @Column(name = "created_on")
    private Date createdOn;

    @Column(name = "created_by")
    private String createdBy;

    @OneToOne(fetch = FetchType.LAZY)
    @MapsId
    private Post post;

    public PostDetails() {}

    public PostDetails(String createdBy) {
        createdOn = new Date();
        this.createdBy = createdBy;
    }

    //Getters and setters omitted for brevity
}

With @MapsId, the id property in the child table serves as both Primary Key and Foreign Key to the parent table Primary Key.

So, if you have a reference to the parent Post entity, you can easily fetch the child entity using the parent entity identifier:

PostDetails details = entityManager.find(
    PostDetails.class,
    post.getId()
);

This way, you won't have N+1 query issues that could be caused by the mappedBy @OneToOne association on the parent side.