@Entity
@Table(name = "orders")
class Order {

    @OneToOne(mappedBy = "order", fetch = FetchType.LAZY, cascade = {CascadeType.ALL})
    private Offer offer;

    public Offer getOffer() {
        return this.offer;
    }

    public void setOffer(Offer offer) {
        this.offer = offer;
    }
}

@Entity
@Table(name = "offers")
class Offer {

}

@Entity
@Table(name = "orders")
class OrderV2 extends Order {

    @OneToMany(mappedBy = "order", fetch = FetchType.LAZY, cascade = {CascadeType.ALL})
    private Set<Offer> offer;

    public Set<Offer> getOffer() {
        return this.offer;
    }

    public void setOffer(Set<Offer> offer) {
        this.offer = offer;
    }
}