在Hibernate中获取JoinColumn ID值而无需查询

Question

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

    private int id;

    //REST OF FIELDS...

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "B_ID", nullable = true)
    private B b;

    //GETTERS AND SETTERS...
}

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

    private int id;
    //REST OF FIELDS...
    //GETTERS AND SETTERS...
}

When I want to get id of B class object related to A class object

//...GETTING A OBJECT FROM DATABASE
B b = a.getB();
if(b != null) {
    int bId = b.getId();
}

Hibernate makes query to database and gets whole B object but i need id only that is in B_ID column in A table.

Is there any way to get B_ID without making additional query ?

Answer 1

If you add

@Column(name = "B_ID", insertable = false, updatable = false)
private int b_id;

and a getter

public int getBId(){
    return b_id;
}

Something similar worked for me at least :)