@Entity
public class B implements Serializable {

    @Id
    @GeneratedValue
    public BigDecimal id;
    @MapsId
    @ManyToOne
    @JoinColumn(name = "id", referencedColumnName = "nonPrimaryRelationId", insertable = false, updatable = false)
    public A a;
}

@Entity
public class A implements Serializable {
    @Id
    @GeneratedValue
    public BigDecimal id;
    @Column
    public BigDecimal nonPrimaryRelationId;
    @OneToMany(fetch = FetchType.LAZY, mappedBy = "a")
    public Set<B> bs;
}