Hibernate的关联映射(4)-单向N-N关联

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单向N-N关联 (必须使用连接表)
Address实体类

package com.anlw.entity;import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.GenerationType;import javax.persistence.Id;import javax.persistence.Table;@Entity@Table(name="address_inf")public class Address {//标识属性@Id@Column(name="address_id11d")@GeneratedValue(strategy=GenerationType.IDENTITY)private Integer addressId;//定义地址详细的成员变量private String addressDetail;//无参构造器public Address(){}//初始化全部成员变量的构造器public Address(String addressDetail) {this.addressDetail = addressDetail;}public Integer getAddressId() {return addressId;}public void setAddressId(Integer addressId) {this.addressId = addressId;}public String getAddressDetail() {return addressDetail;}public void setAddressDetail(String addressDetail) {this.addressDetail = addressDetail;}}

Person实体类

package com.anlw.entity;import java.util.HashSet;import java.util.Set;import javax.persistence.Column;import javax.persistence.Entity;import javax.persistence.GeneratedValue;import javax.persistence.GenerationType;import javax.persistence.Id;import javax.persistence.JoinColumn;import javax.persistence.JoinTable;import javax.persistence.ManyToMany;import javax.persistence.Table;@Entity@Table(name="person_inf")public class Person{//标识属性@Id@Column(name="person_id12")@GeneratedValue(strategy=GenerationType.IDENTITY)private Integer id;private String name;private int age;//定义该Person实体所有关联的Address实体@ManyToMany(targetEntity=Address.class)//映射连接表为p_a@JoinTable(name="p_a",//定义连接表中名为person_id的外键列，该外键列参照当前实体对应表的主键列joinColumns=@JoinColumn(name="p",referencedColumnName="person_id12"),//定义连接表中名为address_id的外键列//该外键列参照当前实体的关联实体对应表的主键列,没有指定unique=trueinverseJoinColumns=@JoinColumn(name="a",referencedColumnName="address_id11d"))private Set<Address> addresses = new HashSet<Address>();public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}public Set<Address> getAddresses() {return addresses;}public void setAddresses(Set<Address> addresses) {this.addresses = addresses;}}

核心测试

package com.anlw.test;import org.hibernate.Session;import org.hibernate.SessionFactory;import org.hibernate.Transaction;import org.hibernate.boot.registry.StandardServiceRegistryBuilder;import org.hibernate.cfg.Configuration;import org.hibernate.service.ServiceRegistry;import com.anlw.entity.Address;import com.anlw.entity.Person;public class Test {public static void main(String[] args) {Configuration conf = new Configuration().configure();ServiceRegistry st = new StandardServiceRegistryBuilder().applySettings(conf.getProperties()).build();SessionFactory sf = conf.buildSessionFactory(st);Session sess = sf.openSession();Transaction tx = sess.beginTransaction();// 创建一个Person对象Person p = new Person();// 创建一个瞬态的Address对象Address a = new Address("guangzhou");// 必须先持久化Address对象sess.persist(a);p.setName("kobe");p.setAge(36);// 设置Person和Address之间的关联关系p.getAddresses().add(a);// 持久化Person对象sess.save(p);// 创建一个瞬态的Address对象Address a2 = new Address("shanghai");// 必须先持久化Address对象sess.persist(a2);// 修改持久化状态的Person对象p.getAddresses().add(a2);tx.commit();sess.close();sf.close();}}

单向的N-N关联和1-N关联的持久化类代码完全相同，控制着关系的一端需要增加一个Set类型的属性，被关联的持久化实例以集合的形式存在；

N-N关联需要使用@ManyToMany注解来修饰代表关联实体的集合属性；

@ManyToMany支持下面属性：

cascade:(非必须属性)指定Hibernate对关联实体采用怎样的级联策略，该级联策略支持如下五个属性：

1.CascadeType.ALL：指定Hibernate将多有的持久化操作都级联到关联实体；

2.CascadeType.MERGE：指定Hibernate将merge操作级联到关联实体；

3.CascadeType.PERSIST：指定Hibernate将persist操作级联到关联实体；

4.CascadeType.REFRESH：指定Hibernate将refresh操作级联到关联实体；

5.CascadeType.REMOVE：指定Hibernate将remove操作级联到关联实体；

fetch:(非必须属性)指定抓取关联实体时的抓取策略，该属性支持如下两个属性值：

1.FetchType.EAGER：抓取实体时，立即抓取关联实体，这是默认值；

2.FetchType.LAZY：抓取实体时，延迟抓取关联实体，等到正真用到关联实体时采取抓取；