Hibernate映射关系之多对多

/**
     * 一个用户可以拥有多个优惠券 但优惠券只有自己的属性，没有用户的引用 单边的一对多关系
     */
    @ManyToMany(fetch = FetchType.EAGER, cascade = { CascadeType.PERSIST })
    @JoinTable(name = "tb_user_coupon", joinColumns = @JoinColumn(name = "user_id", referencedColumnName = "id"), inverseJoinColumns = @JoinColumn(name = "coupon_id", referencedColumnName = "id"))
    // fetch配置加载方式（延迟或即时）
    // cascade配置级联方式,表示在增删查改user类时，会自动在数据库中保存、删除、修改、刷新属于他的Email对象
    private List<Coupon> coupons =new ArrayList<Coupon>() ;

@ManyToMany(mappedBy="coupons")
private Set<User> users=new HashSet<Post>();

@Entity
@Table(name = "tb_user_coupon")
public class UserCoupon {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Integer id;

    @ManyToOne
    @JoinColumn(name = "user_id",nullable=false)
    private User user;
    @ManyToOne
    @JoinColumn(name = "coupon_id",nullable=false)
    private Coupon coupon;

    @Column(updatable = false, nullable = false, columnDefinition = "timestamp default CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP")
    @Temporal(TemporalType.TIMESTAMP)
    private Date createdDate = new Date();

}