JPA @OneToOne或@ManyToOne的延迟获取两个连接列

Question

I have a Topic entity that should correspond to one Questionnaire based on questionnaire version. I need to use lazy fetch.

However, lazy fetch doesn't work. When getting all Topics, I see Hibernate also do individual SQL queries to fetch the questionnaire for each topic.

public class Topic {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "id", nullable = false)
    @Access(AccessType.PROPERTY)
    private long id;

    @Column(name = "questionnaire_version")
    private String questionVer;

    @ManyToOne(optional = true, fetch = FetchType.LAZY)
    @JoinColumns({
            @JoinColumn(name = "id", referencedColumnName = "topic_id",
                insertable = false, updatable = false),
            @JoinColumn(name = "questionnaire_version", referencedColumnName = "version",
                insertable = false, updatable = false)
        })
    @Access(AccessType.PROPERTY)
    private Questionnaire questionnaire;

How do I get lazy fetch working in this case? I need OneToOne here, and I've tried both OneToOne and ManyToOne.

Answer 1

Parent: @OneToOne(optional = true, fetch = FetchType.LAZY, cascade = {CascadeType.ALL})

Child: @ManyToOne(optional = true, fetch = FetchType.LAZY, cascade = {CascadeType.ALL})

Use Cascading either side. You may want to judicially use ALL as per your requirement.