many-to-many

//-----------------------------关联表---------------------------------@Entity@Table(name = "CATEGORY_ITEM")@org.hibernate.annotations.Immutablepublic class CategorizedItem {//使用符合主键    @Embeddable    public static class Id implements Serializable {    @Column(name = "CATEGORY_ID")    protected Long categoryId;    @Column(name = "ITEM_ID")    protected Long itemId;    public Id() {    }    public Id(Long categoryId, Long itemId) {    this.categoryId = categoryId;    this.itemId = itemId;    }    public boolean equals(Object o) {        if (o != null && o instanceof Id) {            Id that = (Id) o;            return this.categoryId.equals(that.categoryId)                && this.itemId.equals(that.itemId);        }        return false;    }    public int hashCode() {        return categoryId.hashCode() + itemId.hashCode();    }    @Column(updatable = false)    @NotNull    protected String addedBy;    @Column(updatable = false)    @NotNull    protected Date addedOn = new Date(); F Maps timestamp    //映射为OneToMany    @ManyToOne    @JoinColumn(    name = "CATEGORY_ID",insertable = false, updatable = false)    protected Category category; G Maps category    @ManyToOne    @JoinColumn(    name = "ITEM_ID",insertable = false, updatable = false)    protected Item item; H Maps item    //值id,由程序生成    @EmbeddedId    protected Id id = new Id();public CategorizedItem(    String addedByUsername,    Category category,    Item item) {    this.addedBy = addedByUsername;    this.category = category;    this.item = item;    this.id.categoryId = category.getId();    this.id.itemId = item.getId();    category.getCategorizedItems().add(this);    item.getCategorizedItems().add(this);    }// ...}//-------------------------两个多对多实体-----------------------------------@Entitypublic class Category {    //放弃管理    @OneToMany(mappedBy = "category")    protected Set<CategorizedItem> categorizedItems = new HashSet<>();    // ...}@Entitypublic class Item {@OneToMany(mappedBy = "item")protected Set<CategorizedItem> categorizedItems = new HashSet<>();// ...}//-------------------------------持久化---------------------------------Category someCategory = new Category("Some Category");Category otherCategory = new Category("Other Category");em.persist(someCategory);em.persist(otherCategory);Item someItem = new Item("Some Item");Item otherItem = new Item("Other Item");em.persist(someItem);em.persist(otherItem);CategorizedItem linkOne = new CategorizedItem("johndoe", someCategory, someItem);CategorizedItem linkTwo = new CategorizedItem("johndoe", someCategory, otherItem);CategorizedItem linkThree = new CategorizedItem("johndoe", otherCategory, someItem);em.persist(linkOne);em.persist(linkTwo);em.persist(linkThree);